AMERICAN 

SULPHURIC  ACID 
PRACTICE 


BY 

PHILIP  DEWOLF 

/' 

AND 

E.  L.  LARISON 

ANACONDA  COPPER  MINING  COMPANY 
WITH  A  SPECIAL  CHAPTER 

BY 

w.  M.  LECLEAR 


FIRST  EDITION 


McGRAW-HILL  BOOK  COMPANY,  INC. 

NEW  YORK:    370  SEVENTH  AVENUE 

LONDON:    6  &  8  BOUVERIE  ST.,  E.  C.  4 

1921 


COPYRIGHT,  1921,  BY  THE 
McGRAw-HiLL  BOOK  COMPANY,  INC. 


TKE  MAFr.fi  PRESS  YORK  PA 


PREFACE 


During  a  period  of  several  years  in  close  contact  with  the 
manufacture  of  Sulphuric  Acid  the  writers  have  a  great  many 
times  been  asked  to  recommend  some  published  work  upon  the 
subject  from  which  a  knowledge  of  the  practical  essentials  of 
modern  American  acid  making  could  be  obtained.  This  inquiry 
has  come  from  men  working  in  association  with,  and  under  the 
supervision  of,  the  writers,  and  also  from  men  in  allied  lines  who 
wished  to  acquaint  themselves  quickly  with  this  information. 

So  far  as  the  writers  know,  such  a  work  in  English  does  not 
exist.  Lunge's  "Sulphuric  Acid  and  Alkali"  is  admirable  in 
many  ways,  and  certainly  every  one  permanently  connected  with 
the  manufacture  of  acid  should  have  it  for  reference :  it  does  not, 
however,  cover  modern  American  practice,  nor  is  it  suitable  to 
present  to  a  new  chamber  operator  as  a  source  of  information. 
Besides  Lunge,  there  are  several  books  which  include  a  few 
chapters  on  sulphuric  acid,  but  none  is  satisfying. 

The  writers'  purpose  in  preparing  this  volume  has  been  to 
provide  some  fundamental  information  for  the  man  with  little 
preliminary  knowledge  of  the  subject.  It  does  not  in  any  way 
pretend  to  cover  acid  manufacture  with  the  thoroughness  of 
Lunge.  History,  chemical  and  physical  theory,  and  many  other 
things  are  treated  from  the  technical,  not  the  scientific,  view-point, 
in  an  effort  to  avoid  the  error,  so  common  in  "  Handbooks,"  of 
not  devoting  much  time  to  Why,  while  very  thoroughly  covering 
How. 

NOTE. — " Sullivan's  Handbook"  so  thoroughly  covers  the 
laboratory  end  that  we  have  not  included  laboratory  practice, 
and  recommend  his  methods. 

The  writers  are  much  indebted  to  several  manufacturers  of 
acid  plant  equipment  for  photographs  and  drawings  of  machinery 
and  apparatus. 

PHILIP    DEWOLP. 
E.  L.  LARISON. 

ANACONDA,  MONTANA, 
April,  1921. 

v 

45G097 


CONTENTS 


PAQK 
PREFACE    v 

CHAPTER 

I.  ALCHEMY,  HISTORY,  DEVELOPMENT,  STATUS 1 

II.  ELEMENTARY  CHEMISTRY  OF  SULPHURIC  ACID 7 

III.  CHARACTERISTICS  AND  USES 16 

IV.  RAW  MATERIALS 44 

V.  PRODUCTION  OF  SO2 49 

VI.  A  BRIEF  DESCRIPTION  OF  THE  CHAMBER  PROCESS 82 

VII.  DUST  SETTLING  APPARATUS 86 

VIII.  THE  GLOVER  TOWER 94 

IX.  THE  CHAMBERS 101 

X.  GAY  LUSSAC  TOWERS 113 

XI.  ACID  CIRCULATION .  118 

XII.  INTRODUCTION  OF  NITRE 136 

XIII.  DRAFT 159 

XIV.  TESTING 166 

XV.  OPERATION 180 

XVI.  CONCENTRATION «  .    .    .    .  189 

XVII.  OUTLINE  OF  THE  CONTACT  PROCESS 207 

XVIII.  PURIFICATION  OF  GASES 217 

XIX.  CONVERTING ......: 228 

XX.  ABSORBTION " 238 

XXI.  CONVERTER  MASS 243 

XXII.  ACCOUNTING 247 

APPENDIX ....-..•. 250 

INDEX  265 


Vll 


AMERICAN 
SULPHURIC  ACID  PRACTICE 

CHAPTER  I 
ALCHEMY,  HISTORY,  DEVELOPMENT,  STATUS 

When  the  old  and  bewhiskered  alchemist  mentally  planned  his 
transmutations  from  lead  to  gold,  he  no  doubt  considered  his 
reagent  "spiritus  vitroli"  second  only  to  his  trusty  Philosopher's 
Stone  in  power  and  usefulness;  for  we  read  of  sulphuric  acid  back 
through  Alchemical  times,  but  the  name  of  the  true  discoverer 
will  probably  always  remain  unknown. 

The  Arabian,  Geber  (A.D.  960),  was  formerly  thought  to 
have  been  the  first  to  describe  the  "spirit  of  alum"  and  its 
solvent  powers,  in  the  mythical  literature  of  the  time,  but  there 
is  a  question  now  whether  this  did  not  creep  in  during  the  Latin 
"translations"  of  the  same.  The  Persian  Alchemist,  Abn-Bekr- 
Alrhases  (A.D.  930),  and  also  DeBeauvais  (A.D.  1240)  are  con- 
ceeded  probable  discovers,  but  direct  evidence  is  woefully  lacking. 

Basil  Valentine  (A.D.  1425),  in  that  landmark  of  Alchemical 
lore,  "The  Triumphal  Car  of  Antimony,"  is  the  first  to  refer  to 
any  method  of  manufacture,  and  therein  describes  the  burning 
of  sulphur  with  saltpeter  in  glass  vessels.  This  method  was 
adopted  by  the  apothecaries  of  the  time,  for  the  manufacture  of 
sulphuric  acid  on  a  small  scale  for  pharmaceutical  use.  From 
the  apothecaries'  laboratory  to  an  industrial  installation  was  the 
logical  sequence,  and  about  1746,  at  Richmond,  near  London,  we 
find  what  was  then  considered  a  large  plant,  operated  by  a  quack 
doctor  named  Ward. 

From  this  point  the  manufacture  branches  off  from  alchemy 
and  quackery,  and  its  development  is  along  scientific  and  me- 
chanical lines.  The  development  and  introduction  of  lead 
chambers  instead  of  glass,  took  place  about  1746,  when  Dr. 
Roebuck,  and  later  a  Mr.  Garbet,  erected  plants  with  lead 
chambers  six  feet  square.  Later  factories  were  built  at  Worces- 
tershire, London,  and  Glasgow. 

1 


2  AMERICAN  SULPHURIC  ACID  PRACTICE 

FIRST  AMERICAN  ACID  PLANT 

The  house  now  known  as  Harrison  Bros.  &  Co.,  Inc.  was 
founded  in  1793  by  Mr.  John  Harrison  of  Philadelphia.  Mr. 
Harrison  received  his  early  education  in  Philadelphia,  and  then 
spent  two  years  in  Europe  investigating  the  arts  and  processes 
of  the  manufacture  of  chemicals  and  in  studying  under  the 
celebrated  chemist,  Dr.  Joseph  Priestley.  Mr.  Harrison  became 
deeply  impressed  with  the  belief  that  many  staples  were  imported 
which  could  be  produced  to  advantage  in  the  United  States, 
thereby  rendering  the  citizens  independent  of  foreign  producers 
and  aiding  the  industrial  development  of  the  youthful  Republic. 
Following  this  thought,  in  1793  he  began  in  Philadelphia  the 
manufacture  of  chemicals,  notably  Sulphuric  Acid,  of  which  he 
was  the  first  maker  in  the  United  States. 

In  that  year,  he  had  a  lead  chamber  capable  of  producing  300 
carboys  per  annum.  The  competition  of  foreign  makers  was  so 
overwhelming  at  first,  that  his  enterprise  was  confined  to  manu- 
facturing for  his  own  use  and  filling  orders  on  a  small  but  very 
remunerative  scale  for  a  few  of  his  patrons,  his  investment  at  the 
start  not  exceeding  $5,000.  In  1807  he  built  what  was  for  that 
time  quite  a  large  lead  chamber;  it  was  50  ft.  long,  18  ft.  wide  and 
18  ft.  high  and  capable  of  making  nearly  half  a  million  pounds  of 
Sulphuric  Acid  annually,  the  price  of  the  staple  being  then  as 
high  as  15c.  per  pound.  According  to  a  letter  addressed  by  Mr. 
Harrison  to  President  Jefferson,  dated  November  1,  1808,  and 
now  in  the  archives  of  the  State  Department  at  Washington,  it  is 
learned  that  he  had  then  developed  his  Sulphuric  Acid  Plant  to 
such  an  extent  as  to  have  a  possible  annual  output  of  3,500 
carboys  and  he  had  also  extended  the  line  of  products  in  his 
laboratory  by  adding  the  various  preparations  of  mercury, 
antimony,  copper,  etc.,  used  in  the  arts  and  medicines  at  an 
investment  of  some  $40,000.  This  was  at  his  establishment  on 
Green  Street,  west  of  Third. 

As  is  well  known,  acid  produced  in  lead  chambers  is  not  the 
Oil  of  Vitriol  of  commerce  and  the  only  method  known  at  that 
time  to  concentrate  it  to  the  required  strength  was  by  boiling  it 
in  glass  retorts — a  very  precarious  and  dangerous  process.  The 
constant  breakage  of  the  glass  largely  increased  the  cost  of  the 
concentrated  acid  and  the  dangers  of  the  work.  To  obviate  this 
great  trouble  Mr.  Harrison,  in  1814,  introduced  the  use  of  Plati- 


ALCHEMY,  HISTORY,  DEVELOPMENT,  STATUS  3 

>-*' 

num  for  the  manufacture  of  Sulphuric  Acid,  for  the  first  time,  at 
least  in  this  country.  In  the  previous  year,  1813,  Dr.  Eric 
Bollman,  a  Dane,  had  come  to  Philadelphia.  Dr.  Bollman  was 
familiar  with  the  metallurgy  of  platinum  and  a  highly  scientific 
man.  He  brought  with  him  from  France  Dr.  Wollaston's 
method  for  converting  the  crude  grains  of  platinum  into  bars 
and  sheets.  About  the  first  use  that  Dr.  Bollman  made  of  these 
platinum  sheets  was  the  construction,  early  in  1814,  of  a  still  for 
the  concentration  of  Sulphuric  Acid  for  the  Harrison  Works.  It 
weighed  700  oz.,  had  a  capacity  of  25  gal.,  and  was  in  continuous 
use  for  15  years.  This  early  application  of  platinum  for  such 
purposes  was  highly  characteristic  of  the  sagacity  and  ingenuity 
of  the  American  manufacturer.  At  the  time  the  use  of  this  rare 
metal  was  a  novelty  in  Europe  and  known  only  to  a  few  persons 
and  certainly  entirely  unknown  in  this  country.  It  follows, 
therefore,  that  Mr.  John  Harrison  was  not  only  the  earliest 
successful  manufacturer  of  Sulphuric  Acid  in  America,  but  the 
first  in  this  country  to  concentrate  it  in  platinum.  Too  great 
praise  cannot  be  given  him  for,  as  Liebig  has  said,  "The  quantity 
of  Sulphuric  Acid  made  in  a  country  is  a  sure  index  to  its  wealth 
and  prosperity." 

In  1806,  Mr.  Harrison  began  the  manufacture  of  white  lead 
and  he  and  his  successors  have  continuously  marketed  their 
product  since  that  date.  In  fact,  with  one  exception,  the  "Harri- 
son" lead  is  the  oldest  established  brand  of  white  lead  in  the 
United  States.  In  later  years,  he  introduced  into  his  works 
apparatus  for  making  pyroligneous  and  acetic  acids  and  their 
dependent  products,  white  and  brown  sugar  of  lead,  also  oxides 
of  lead,  colors,  alum,  coppers,  iron  liquors,  etc.  Mr.  Harrison 
may  be  credited  with  doing  more  to  influence  the  establishment 
and  development  of  the  chemical  industries  than  almost  any 
man  of  his  time. 

The  Green  Street  Works  soon  grew  too  small  for  such  large 
operations  as  Mr.  Harrison  had  undertaken  and  an  eligible  loca- 
tion was  secured  in  Kensington,  now  the  Eighteenth  Ward  of 
this  city,  where  extensive  buildings  were  erected  and  large  manu- 
facturing facilities  provided.  In  1831  he  admitted  his  sons  to 
partnership,  under  the  title  of  John  Harrison  &  Sons.  He  died 
in  1833  and  in  that  year  the  firm  name  was  changed  to  Harrison 
Brothers.  In  1859,  by  the  admission  of  the  founder's  grandsons, 
John  Harrison,  George  L.  Harrison  and  Thomas  S.  Harrison,  the 


4  AMERICAN  SULPHURIC  ACID  PRACTICE 

firm  name  became  Harrison  Bros.  &  Company  and  in  1898  was 
incorporated.  In  1917  the  Greys  Ferry  plant  was  taken  over 
by  the  Du  Pont  Company  and  is  now  known  as  the  Harrison 
Works. 

Holker,  in  1766,  introduced  the  first  lead  chambers  into  France, 
and  at  his  Rouen  plant  the  two  important  ideas  of  introducing 
steam  into  the  chambers  during  combustion,  and  continuous  air 
feed,  were  mechanically  developed.  In  Germany  the  first  lead 
chambers  were  probably  those  at  Ringkuhl,  near  Cassel.  Dr. 
Richard's  plant  near  Dresden  (1820)  was  one  of  the  oldest,  and 
although  it  was  erected  some  time  after  the  idea  of  continuous 
air  feed  had  been  perfected,  it  represented  the  old  intermittent 
type. 

The  last  150  years  has  seen  little  or  no  change  in  the  funda- 
mental idea  of  the  English,  or  chamber  process.  True,  the 
chambers  have  been  increased  tremendously  in  size,  the  genera- 
tion of  S02  has  undergone  marvelous  mechanical  development, 
and  the  utilization  of  valuable  waste  products  has  become  of 
great  importance;  methods  of  handling  the  product  have  been 
rendered  many  times  more  efficient:  but  for  the  original  idea 
we  are  indebted  to  the  pseudo-scientists  of  the  Alchemical  period. 

One  of  the  promoters  of  the  Contact  Process  once  said,  "The 
alchemists  and  the  early  English  chemists  could  hardly  have 
helped  stumbling  onto  the  discovery  and  manufacture  of  oil  of 
vitriol  by  the  Chamber  Process,  but  it  remained  for  a  nation  of 
real  scientists  to  discover  and  develop  the  Contact  Process."  For 
nowhere  in  the  field  of  industrial  chemistry  can  the  chemical 
engineer  see  so  clearly  the  result  of  systematic,  painstaking 
research,  experiment,  and  accurate  interpretation  of  observation. 

Up  to  the  close  of  the  eighteenth  century  the  little  fuming  acid 
demanded  by  the  arts  had  been  produced  almost  exclusively  by 
the  firm  of  Joseph  Starck,  in  Bohemia,  by  the  distillation  of  dry 
ferrous  sulphate  and  the  absorption  of  the  evolved  SO 3  in  a  high 
strength  pan  concentrated  acid.  From  the  place  where  it  was 
stored  it  was  called  Nordhausen  acid. 

About  1875,  Cl.  Winkler,  and  later  Squire  and  Wessel,  showed 
that  SO3  is  easily  formed  by  the  interaction  of  S02  and  02,  in  the 
presence  of  a  number  of  substances  in  a  finely  divided  state,  with 
certain  other  requirements  as  to  temperature,  humidity,  and 
pressure.  Although  the  oxides  of  iron  and  cobalt,  and  metallic 
gold,  iridium,  and  silicon  produce  this  result,  none  of  them 


ALCHEMY,  HISTORY,  DEVELOPMENT,  STATUS  5 

approach  the  efficiency  of  conversion  obtained  with  small  per- 
centages of  metallic  platinum.  The  platinum  itself  is  unacted 
upon  and  termed  a  catalyzer,  after  the  suggestion  of  Berzilius, 
in  1835. 

The  commercialization  of  Winkler's  idea  has  been  rapid  during 
the  last  forty  years,  owing  to  the  increased  demands  of  the  dye 
makers  and  oil  refiners,  so  that  today  the  old  distillation  process 
is  obsolete. 

About  1875,  the  promoters  of  the  process  that  later  became 
known  as  the  Hanish  and  Schroder,  using  Winkler's  ideas, 
secretly  tried  out  the  catalysis  of  SO3,  using  first  pure  S02  and 
oxygen,  and  later  dilute  SC>2  from  pyrites,  with  platinized  asbestos 
as  the  catalytic  agent,  and  a  heated  entrance  gas,  under  a  pressure 
of  three  atmospheres. 

But  the  great  obstacles  in  the  way  of  the  development  of  the 
process  were  the  failure  to  get  a  dry  and  arsenic  free  entrance  gas, 
the  false  idea  that  SO2  and  oxygen  must  be  present  in  stoichi- 
ometrical  proportions,  and  that  nitrogen  was  detrimental.  These 
three  difficulties  alone  must  be  considered  the  causes  of  the  failures 
of  the  pioneers,  and  the  financial  losses  through  semi-commercial 
experiments  were  startling. 

Through  the  disloyalty  of  a  workman  at  the  Badische  works 
(Ludwigshaven)  the  important  secrets  of  their  process  were  ob- 
tained by  their  competitors,  and  simultaneously,  1898,  patents 
were  issued  to  three  different  companies:  THE  BADISCHE  ANILIN 

UND    SODAFABRIK    OP  LUDWIGSHAVENJ   THE    FARBEWERKE   VORM 

MEISTER,  Lucius  &  BRUNING,  OF  HOCHST;  AND  THE  VEREIN 
CHEMISCHER  FABRIKEN  OF  MANHEIM. 

These  three  companies  at  once  set  about  the  commercial  per- 
fection of  the  process,  as  secretely  as  possible,  the  only  important 
variation  being  in  the  catalytic  agent.  To  trace  the  foreign 
development  would  indeed  be  interesting,  but  we  are  limited  by 
title  to  American  practice. 

American  manufacturers,  due  to  their  lack  of  appreciation  of 
the  results  of  organized  research  and  experiment,  refused  to 
finance  any  work  along  these  lines,  and  followed  the  usual  course 
of  importing  the  developed  process  and  trained  men  for  install- 
ations in  this  country.  The  Schroder  process,  employing 
platinized  magnesium  sulphate,  and  the  Badische,  with  platinized 
asbestos,  have  been  the  most  favored  in  America. 

An  eminent  chemical  engineer  has  called  sulphuric  acid  the 


6  AMERICAN  SULPHURIC  ACID  PRACTICE 

back  bone  of  the  chemical  industry,  for  like  soda,  its  uses  are  so 
diversified  and  its  production  so  great,  that  in  any  country  it  is 
a  true  barometer  of  chemical  and  industrial  progress.  It  finds 
its  greatest  use  in  fertilizer  manufacture  (80  per  cent),  and  is 
indispensable  in  the  manufacture  of  coal  tar  dye  stuffs,  petroleum 
products,  paper,  stearine,  oleine,  sodium  sulphate,  soda;  hydro- 
chloric, nitric,  citric,  and  tartaric  acids;  sulphates  of  iron  and 
copper;  alums,  shoe  blackings,  coke  plant  by-products,  electro- 
lytic refining  of  metals,  mostly  copper;  it  enters,  directly  or 
indirectly,  into  almost  every  chemical  process.  In  some  of  the 
more  important  branches  of  the  chemical  industry  it  is  a  raw 
material  costing  millions.  The  amounts  used  in  the  manufacture 
of  explosives,  during  the  late  War,  were  enormous.  This  huge  war 
increase  was  of  course  only  temporary,  and  there  are  many  plants, 
paid  for  by  the  War,  that  should  make  very  cheap  acid. 

While  the  Contact  process  has  many  advantages  over  the 
Chamber  process,  such  as  no  bulky  chambers  of  concentration 
pans,  it  is  very  doubtful  if  it  will  ever  completely  replace  the 
chambers.  It  cannot  make  50°  and  60°  Be.  acids  to  compete, 
and  requires  some  method  of  producing  weak  acid  to  keep  it 
going.  But  on  the  production  of  higher  strength  acids  it  is 
supreme,  and  statistics  show  that  it  is  gaining  in  the  United  States 
today.  The  cost  of  platinum  for  concentrating  pans  is  excessive 
and  increasing,  and  that  required  for  contact  mass  is  negligible 
in  comparison.  Both  processes  are  being  improved  steadily, 
and  the  patent  rights  are  costing  less  each  year,  and  in  a  few  years 
will  become  public  property.  Supervision,  regulation  and  yield 
are  all  better  on  the  contact  process,  while  depreciation  and 
maintainance  are  less. 

In  April,  1920,  the  Department  of  Commerce  had  no  figures  for 
production  since  1915.  They  show  a  25  per  cent  increase  in 
production  during  1915  over  the  previous  year,  and  one  war  time 
plant  alone,  completed  in  1916,  produced  a  quarter  of  a  million 
tons  of  fuming  acid  a  year,  against  49,000  tons  for  the  whole 
country  in  1914. 

A  few  figures  on  the  world's  production  will  give  an  idea  of  the 
rate  of  development : 

1880  1,850,000  tons 

1892  2,818,000  tons 

1902  4,450,000  tons 

1909  8,000,000  tons 


CHAPTER    II 
ELEMENTARY  CHEMISTRY  OF  SULPHURIC  ACID 

When  sulphur,  either  brimstone  or  a  metallic  sulphide,  is 
burned  in  air,  sulphur  dioxide,  SO2,  is  produced.  This  is  the 
starting  point  of  the  sulphuric  acid  industry. 

SO2  is  a  colorless  gas  of  a  suffocating  odor,  and  will  not  burn 
nor  support  combustion  directly,  under  ordinary  conditions.  It 
is  very  injurious  to  plants.  It  contains  50.05  per  cent  sulphur, 
and  49.95  per  cent  oxygen.  Molecular  weight,  64.04  per  cent. 
Specific  gravity,  2.2136.  A  liter  of  S02  at  O°C.  and  760  mm. 
pressure  weighs  2.8608  g.  Its  heat  of  formation  is  given 
(Richards)  as  69,260  as  a  gas,  or  77,600  in  dilute  solution. 

Anhydrous  sulphur  dioxide  will  not  act  upon  iron,  up  to  100°C., 
but  the  commercial  product,  containing  up  to  the  1  per  cent 
H2O  that  it  carries  at  saturation,  does  act  slightly. 

Owing  to  the  catalytic  action  of  the  hot  iron  of  the  burners, 
some  SO 3  is  formed  when  brimstone  is  burned  but  not  enough  to 
influence  the  process.  With  pyrites,  however,  the  SO3  formed  is 
considerable,  as  the  catalytic  action  of  the  red  hot  iron  oxides  is  very 
marked;  in  fact  the  oxides  of  iron,  copper  and  chromium  are  the 
only  catalytic  (?)  agents  that  have  been  seriously  experimented 
with,  outside  of  platinum.  The  generally  accepted  theory  for 
the  action  of  the  metallic  oxides  is  that  they  are  more  oxygen 
carriers  than  actual  catalyzers:  doing  their  work  more  as  the 
nitrogen  oxides  do  theirs,  than  as  platinum  does  its  work. 

The  yields,  when  ferric  oxide  is  used,  are  not  high  enough  to 
permit  it  to  seriously  compete  with  platinum  as  the  catalytic 
agent  used  in  this  industry,  in  the  present  state  of  our  knowledge. 

The  reactions  are  probably  two,  both  taking  place  at  very 
nearly  the  same  temperature,  viz. : 

2Fe,O8  +  3O2  +  6SO2  =  2Fe2(S04)3 

which  splits  up  into 

Fe2O3  +  3S03 

the  Fe20g  being  ready  to  repeat  the  cycle 

7 


8  AMERICAN  SULPHURIC  ACID  PRACTICE 

and  3Fe203  +  S02  =  2Fe304  +  S03 

and  4Fe304  +  02  =  6Fe203 

when  the  Fe2O3  is  again  ready  to  repeat. 

SO2  is  pretty  soluble  in  water,  one  volume  of  water,  at  atmos- 
pheric pressure,  and  32°F.,  dissolving  about  80  volumes  SO2. 
However,  this  does  not  appear  to  be  a  chemical  compound, 
H2SO3,  sulphurous  acid,  because  S02  evaporates  from  it  even  at 
ordinary  temperatures. 

Bunsen  and  Schonfeld  published  the  following  table,  in  1905, 
of  the  solubility  of  S02  in  water,  at  760  mm.  pressure: 

TABLE  1 

TEMPEBATUBE,  1  LITEB  HkO  DISSOLVES 

°C  LITERS  SOj 

0  79.8 

5  57.5 

10  56.6 

15  47.3 

20  39.4 

Solutions  of  S02  slowly  oxidize  in  the  presence  of  air. 

Sulphuric  acid  is  a  compound,  in  varying  proportions,  of 
sulphur  trioxide  and  water.  Several  different  compounds  exist, 
showing  all  the  properties  of  definite  chemical  compounds.  The 
mono-  and  the  duo-hydrates  have  been  the  most  frequently 
studied.  Acid  of  a  concentration  of  98.3  per  cent  or  better 
seems  to  hold  the  1.7  per  cent  or  less  of  water  present  chemically, 
and  this  is  the  absolute  limit  to  which  a  concentration  by  distilla- 
tion can  go.  In  practice,  98  per  cent  is  rarely  reached,  however. 

Sulphuric  acid  has  a  tremendous  affinity  for  water,  combining 
with  it  violently,  with  evolution  of  great  heat.  Of  the  entire 
molecular  heat  of  formation,  192,200  calories,  100,300  calories, 
or  53.5  per  cent,  results  from  the  combination  of  the  anhydrous 
SO 3  with  the  water.  A  very  common  manifestation  of  this 
affinity  is  the  charring  of  carbo-hydrates  by  sulphuric  acid,  the 
water  in  the  combination  being  removed,  leaving  the  carbon 
behind. 

Another  familiar  result  of  this  affinity  is  the  dense  white 
cloud  that  forms  when  SO 3  escapes  into  the  air.  Air  at  all  times 
contains  moisture-humidity  and  the  S03  combining  with  this 
moisture  forms  H2S04  in  minute  particles.  These  particles  are 


ELEMENTARY  CHEMISTRY  OF  SULPHURIC  ACID  9 

small  enough  to  remain  suspended  in  the  air  for  a  long  time,  form- 
ing a  white  cloud,  or  "fume"  not  properly  a  fume  at  all,  because 
it  is  not  a  gas,  but  a  mass  of  small  liquid  particles. 

As  there  is  always  some  moisture  in  the  air  we  always  have  an 
indicator  as  to  whether  S03  is  going  through  our  system  and 
being  lost  out  our  stacks.  While  "fumes"  come  from  other 
causes,  if  there  is  no  "fume"  there  is  no  SO3  escaping. 

The  moisture  in  the  air  has  a  very  direct  effect  upon  the  contact 
process  in  keeping  down  the  strength  of  the  acid  that  can  be 
made.  The  air  introduced  into  the  system  carries  with  it  its 
own  share  of  humidity,  which  must  be  absorbed,  and  thus  dilute 
the  acid  made.  In  the  Middle  Atlantic  States  this  will  average 
60  Ib.  of  water  per  ton  of  100  per  cent  acid  made,  or  3  per  cent: 
less  in  winter,  and  more  in  summer,  for  the  saturation  point  of 
air  increases  rapidly  with  the  temperature.  Consequently,  if  it 
is  desired  to  make  very  high  concentration  fuming  the  location 
must  be  in  the  driest  climate  possible. 

There  are  three  distinct  steps  in  the  evolution  of  sulphur  into 
sulphuric  acid,  either  naturally,  or  directed  by  man.  They  are 
the  burning  of  the  sulphur  to  SO2,  the  oxidation  of  the  dioxide 
to  the  trioxide,  and  the  hydrating  of  this  trioxide. 

In  the  chamber  process  the  last  two  steps  proceed  simultane- 
ously, the  water  acting  both  as  an  assistant  to  the  catalyser, 
various  oxides  of  nitrogen,  and  as  the  hydrator.  The  oxidation 
will  not  proceed  at  a  commercially  practicable  rate  unless  water 
is  present  in  excess,  consequently  the  acid  produced  is  dilute, 
,  and  to  make  strong  acid  must  be  concentrated. 

We  know  what  results  may  be  attained  by  different  methods 
of  handling  the  process,  but  the  intermediate  changes  that  occur 
are  the  subjects  of  very  heated  controversy.  There  is  no  doubt 
that  nitrososulphuric  acid,  SO2(OH)(ONO)  is  formed,  which 
breaks  up  into  H2SO4  and  NO.  The  NO  becomes  oxidized  to 
NO2,  N2O3,  and  N204,  probably  a  mixture  of  all  three,  and  HNO3, 
deriving  the  oxygen  from  the  excess  of  air  present,  and  the  H2SO4 
immediately  takes  up  an  excess  of  water  and  condenses. 

In  a  work  of  this  character,  written  as  an  operating  handbook, 
not  as  a  treatise,  it  would  not  serve  any  useful  purpose  to  go  into 
the  theories  of  Weber,  Winkler,  Raschig,  and  Lunge,  regarding 
changes  within  the  chambers. 

The  saving  of  the  nitrogen  oxides  is  of  the  uttermost  import- 
ance, as  without  this  saving  the  process  would  not  be  com- 


10  AMERICAN  SULPHURIC  ACID  PRACTICE 

mercially  practicable.  The  Gay-Lussac  tower  was  the  first 
nitrate  saver,  and  now,  in  conjunction  with  the  Glover  tower, 
reduces  the  nitrate  from  11  per  cent  to  4  per  cent. 

Strong  sulphuric  acid  absorbs  nitrous  acid,  forming  nitroso- 
sulphuric  acid  as  follows: 

2H2S04  +  N2O3  =  2SO2(OH)(ONO)  +  H2O 

it  absorbs  nitric  peroxide,  forming  nitrososulphuric  acid  and 
nitric  acid : 

H2S04  +  N204  =  S02(OH)(ONO)  +  HN03 

Nitrososulphuric  acid  is  decomposed  by  water  alone,  (1)  or 
by  water  and  S02,  (2) : 

(1)  2SO2(OH)(ONO)  +  H20  =  2H2SO4  +  N2O3 

(2)  2S02(OH)(ONO)  +  S02  +  2H20  =  3H2S04  +  2NO 

and  the  nitric  oxides  are  ready  to  repeat. 

The  recovery  of  the  nitrogen  gases  is  accomplished  by  taking 
advantage  of  two  of  the  reactions  that  proceed  within  the 
chamber — the  absorbtion  of  N2O3  and  N2O4,  in  the  Gay-Lussac 
tower,  by.  strong  sulphuric  acid,  and  the  decomposition  of  the 
product,  at  a  point  where  it  is  available,  by  burner  gas,  (SO2), 
to  H2SO4  and  NO. 

N203  and  N2O4  are  absorbed  by  strong  sulphuric  acid,  forming 
nitrososulphuric  acid,  as  shown  in  the  reactions  of  the  chamber. 
This  prevents  the  escape  of  the  nitrogen  gases  into  the  atmos- 
phere, with  the  attendant  loss  of  nitre  and  the  damage  done,  but 
the  nitrososulphuric  acid  is  of  little  value,  and  must  be  made 
into  a  useful  product. 

The  Glover  tower  accomplishes  this.  As  shown  in  the  chamber 
reactions,  water  and  SO2  decompose  SO2(OH)(ONO) — nitroso- 
sulphuric acid — to  H2SO4  and  NO,  so  by  bringing  the  hot  burner 
gases,  rich  in  S02,  in  contact  with  the  nitrososulphuric  acid  that 
reaction  is  brought  about,  and  in  addition  the  heat  present  effects 
a  considerable  concentration,  the  water  from  the  concentrated 
acid  going  on  with  the  burner  gas  and  the  NO  back  to  the 
chambers,  thus  being  used  over  and  over  again. 

CONTACT  PROCESS 

In  the  contact  process  S02  is  produced  by  the  same  means  that 
are  employed  to. make  it  for  chambers.  The  last  two  steps  are 
separate  and  distinct,  however,  and  instead  of  an  excess  of  water, 


ELEMENTARY  CHEMISTRY  OF  SULPHURIC  ACID         11 

giving  a  dilute  acid,  there  is  an  excess  of  SO3,  producing  fuming 
acid. 

Burner  gases  must  be  cleaned  of  certain  impurities,  before 
touching  the  catalytic  agent,  which  in  this  country  is  always 
finely  divided  platinum,  on  either  asbestos  or  roasted  magnesium 
sulphate. 

The  following  is  from  a  paper  by  Dr.  Charles  L.  Reese,  Journal 
of  the  Society  of  Chemical  Industry,  March  31,  1906: 

"  Water — it  was  thought  at  one  time  to  be  essential  that  the  gases 
be  dried  by  sulphuric  acid  not  weaker  than  60°Be\,  but  this  was  found 
to  be  an  error,  in  that  the  gases  could  be  saturated  with  moisture,  by 
passing  them  through  water  before  introduction  into  the  contact  mass, 
without  affecting  the  conversion  in  any  way.  Fuming  sulphuric  acid 
was  produced,  but,  of  course,  such  a  procedure  could  not  be  carried 
out  on  a  manufacturing  scale,  where  it  is  necessary  to  use  iron  pipes. 

"Carbon  dioxide  had  no  effect  whatever,  whenever  introduced  into 
the  gas,  as  was  to  be  expected,  but  I  was  surprised  to  find  that  carbonic 
oxide  had  no  deleterious  effect,  in  spite  of  its  reducing  qualities.  On 
one  occasion  the  conversion  in  a  certain  plant  ceased  altogether,  and 
we  were  at  a  loss  to  know  the  cause.  We,  however,  soon  found  that 
some  coal  had  got  mixed  with  the  pyrites  in  the  burners.  In  this  case 
there  was  carbon  dioxide,  and  possibly  carbonic  oxide,  present,  but 
there  was  also  evidently  a  lack  of  oxygen,  and  when  the  coal  was  con- 
sumed, conversion  began  again. 

"  Sulphur  will  at  times  find  its  way  through  two  or  three  scrubbing 
towers,  and,  before  the  filtering  system  was  adopted,  it  became  neces- 
sary to  determine  whether  the  presence  of  sulphur  in  the  gas  would 
affect  the  catalytic  action  of  the  contact  material.  Experiments  were 
carried  out  to  determine  this  point.  It  was  desirable  to  introduce  sul- 
phur into  the  gas  in  as  finely  divided  condition  as  possible.  This  was 
accomplished  by  introducing  hydrogen  sulphide  into  the  gas.  When 
hydrogen  sulphide  is  mixed  with  sulphur  dioxide  the  reaction  between 
these  two  gases  takes  place,  producing  sulphur  and  water,  and  thus 
sulphur  was  introduced  into  the  mass.  It  was  found,  on  discontinuing 
the  introduction  of  hydrogen  sulphide,  the  conversion  continued  to  be 
normal,  and  the  sulphur  was  simply  carried  through  the  tube.  This 
experiment  was  repeated  a  number  of  times  with  the  same  result,  show- 
ing that  the  presence  of  sulphur  does  not  affect  the  reaction.  Of  course, 
hydrogen  sulphide  would  affect  it,  in  that  it  would  reduce  the  sulphur 
dioxide. 

"The  above  substances  do  not  affect  the  reaction  of  the  contact  mass, 
but  hydrochloric  acid,  chlorine,  silicon  tetra-fluoride,  arsenic,  and  lead 
do  seem  to  affect  it  in  two  distinct  ways:  first,  by  their  presence  in 


12  AMERICAN  SULPHURIC  ACID  PRACTICE 

the  gas,  and  only  when  present  in  the  gas;  arid  second,  affecting  the 
catalytic  property  of  the  contact  material.  In  the  first  case  we  have 
hydrochloric  acid,  chlorine,  and  silicon  tetra-fluoride.  In  the  second  we 
have  arsenic  and  lead. 

"When  Hydrochloric  Acid  gas  is  introduced,  the  effect  is  instantaneous, 
reducing  the  conversion  from  98.5  per  cent  to  42  per  cent,  but  when  the 
hydrochloric  acid  gas  is  discontinued  and  air  passed  through  for  a  while 
to  displace  it,  the  conversion  becomes  normal  in  a  short  time. 

"The  presence  of  Chlorine  in  the  gas  seems  to  have  an  effect  similar 
to  that  of  hydrochloric  acid,  although  not  so  intense.  In  both  cases 
the  dry  chlorine  or  the  hydrochloric  acid  was  introduced,  until  a  mini- 
mum yield  was  obtained,  which  in  the  case  of  HC1  was  about  42  per 
cent,  and  that  of  the  Cl  was  57  per  cent.  After  discontinuing  the  HC1 
and  the  Cl,  air  was  passed  through  and  the  operation  was  continued  at 
the  same  temperature.  As  will  be  seen  by  the  curve  the  percentage 
conversion  gradually  arose  again  to  the  normal.  Although  at  one  point 
the  gas  showed  a  trace  of  HC1,  the  conversion  amounted  to  94  per  cent. 

"The  introduction  of  a  small  quantity  of  silicon  tetra-fluoride  caused 
the  conversion  to  drop  immediately,  but  on  discontinuing,  the  conver- 
sion rose  in  a  few  minutes  to  normal.  In  each  case  some  silica  was  un- 
doubtedly deposited  upon  the  contact  mass,  but  most  of  it  passed 
through  the  tube,  as  was  made  evident  by  the  fact  that  the  silica  sepa- 
rated out  when  the  gas  came  in  contact  with  the  water  solution  used  in 
testing  the  exit  gas.  Of  course  a  minute  quantity  of  silicon  tetra- 
fluoride  in  the  gas  would  gradually  deposit  silica  on  the  contact  mass, 
and  would  eventually  cover  the  contact  agent,  so  as  to  render  it  inactive ; 
but  when  contact  mass  is  so  affected  it  can  be  easily  rendered  active  by 
simply  removing  it  from  the  converter  and  putting  it  back  again.  The 
handling  will  be  sufficient  to  expose  surfaces. 

"The  injurious  effect  of  arsenic  upon  the  contact  mass  is  extremely 
marked.  Arsenious  acid  was  placed  in  the  front  end  of  the  tube,  heated, 
and  carried  into  the  contact  tube  by  the  flow  of  gas.  The  effect  of  the 
arsenic  was  to  reduce  the  conversion  absolutely  to  zero,  owing  to  the 
large  amount  introduced,  but  after  40  min.  it  rose  again  to  40  per  cent. 
At  this  time  HC1  was  introduced  for  50  min.  to  remove  the  arsenic,  and 
then  air  drawn  through  for  15  min.  more.  The  process  was  then  con- 
tinued, and  the  conversion  then  rose  to  96.5  per  cent.  Several  attempts 
were  made  to  find  a  simple  means  of  removing  As  from  the  contact 
mass,  and  at  first  Cl  was  used  for  this  purpose.  The  mass  was  placed 
in  a  tube,  heated,  and  Cl  passed  through.  This  did  remove  some  of 
the  As,  but  did  not  regenerate  the  mass  sufficiently.  A  very  interest- 
ing observation  was  made,  however,  during  this  experiment.  It  was 
found  the  Cl  carried  over  platinum  to  the  exit  end  of  the  tube,  and 
deposited  it  in  the  form  of  a  chloride.  This  was  done  at  a  temperature 
of  400°-450°C. 


ELEMENTARY  CHEMISTRY  OF  SULPHURIC  ACID        13 

"It  was  found  in  attempting  to  regenerate  or  remove  arsenic,  that 
HC1  mixed  with  the  reduced  sulphurous  gas  was  much  more  effective, 
as  is  shown  by  the  curve  referred  to,  all  arsenic  having  been  removed. 

"It  is  well  known  that  when  platinum  is  heated  in  the  presence  of 
lead  or  lead  salts,  lead  combines  with  the  platinum  either  to  form  an 
alloy  or  a  compound,  and  this  combination  of  lead  with  platinum  un- 
doubtedly destroys  the  catalytic  property  of  the  platinum.  The  effect 
of  lead,  however,  was  not  determined  in  the  regular  way,  but  can  be 
shown  very  readily  by  one  or  two  experiments. 

"It  is  well  known  that  when  a  platinum  spiral  is  heated  in  a  gas  flame, 
the  gas  turned  off  for  a  few  minutes,  and  on  again,  the  spiral  will  reignite 
the  gas.  A  small  piece  of  contact  mass  will  do  the  same,  but  if  either 
is  moistened  with  a  small  quantity  of  lead  acetate  and  then  ignited,  it 
will  lose  this  property  of  reigniting  gas,  unless  it  is  heated  sufficiently 
long  to  volatilize  the  lead.  A  similar  experiment  will  show  in  a  rough 
way  the  effect  of  arsenic  on  contact  mass  or  a  platinum  spiral." 

The  above  quotation  shows  very  clearly  the  necessity  for 
very  careful  scrubbing.  The  loss  of  sulphur,  and  consequently 
of  acid,  from  unconverted  S02  that  passes  on  out  the  stacks 
is  anywhere  from  60  per  cent  to  80  per  cent  of  the  entire  loss, 
and  anything  that  throws  the  mass  off  at  all  will  enormously 
increase  that  loss.  The  operation  costs  the  same,  with  the 
exception  of  the  small  item  of  handling  the  finished  acid,  with 
a  low  as  with  a  high  conversion  and  the  yield,  and  consequently 
the  income,  is  cut  down  in  the  proportion  that  the  conversion  falls 
off. 

Arsenic  is  by  all  odds  the  worst  of  the  contact  "poisons"  with 
which  we  have  to  deal. 

Opl's  theory  is  that  the  destruction  of  the  activity  of  the 
contact  mass  is  caused  by  the  deposition  of  a  glass-like  coating 
over  the  platinum,  thus  mechanically  preventing  its  contact 
with  the  gas.  This  coating  is,  he  says,  a  deposition  product  of 
As2O3  and  SOs,  with  a  formula  3As2O3,  2SOs.  Lunge  says  this 
product  has  actually  been  found  in  dust  chambers. 

Dr.  Krauss  holds  that  the  arsenic  is  oxidized  to  a  non-volatile 
oxide,  which  combines  with  platinum. 

In  a  plant  on  the  Pacific  coast,  operating  on  the  Schroeder- 
Grillo  process,  using  pyrites,  it  is  necessary  to  regenerate  the 
mass  about  every  four  weeks,  and  an  astonishing  fact  has  been 
noted — that  while  the  platinum  recovers  its  activity,  the  arsenic 
remains  in  the  mass.  It  appears  to  exist  after  the  regeneration 
in  the  form  of  Realgar,  arsenic  disulphide,  As2S2,  and  in  that 


14  AMERICAN  SULPHURIC  ACID  PRACTICE 

form  is  apparently  not  a  contact  poison.  I  have  been  informed 
that  after  3  years  the  quantity  of  arsenic  in  the  mass  is  actually 
greater  than  the  amount  of  platinum,  but  the  old  arsenic  seems 
to  be  perfectly  inert,  having  no  effect,  good  or  bad,  and  it  is  not 
until  fresh  arsenic  compounds  are  introduced  that  the  mass  again 
loses  its  activity. 

Of  course  there  is  a  loss  of  the  efficiency  of  the  mass  in  regen- 
erating, because  the  platinum  becomes  distributed  through  the 
grains  of  magnesium  sulphate,  instead  of  all  being  on  the  outside, 
thus  reducing  the  area  that  can  come  in  contact  with  the  gas. 

The  absorbtion  system  requires  conditions  proper  for  the 
combination  of  SO3  and  H20.  The  principal  interferences  with 
these  conditions  are  vapor  pressures,  as  follows: 

(a)  Vapor  pressure  due  to  H20, 

(b)  Vapor  pressure  due  to  SO3,  and 

(c)  Vapor  pressure  due  to  foreign  acids,  as  HN03  or  HC1. 

Heat  increases  vapor  pressures,  so  temperature  control  is 
necessary. 

The  vapor  pressure  due  to  H2O  exists  when  the  strength  of 
the  absorbing  acid  drops  below  98.3  per  cent  H2SO4.  Above 
that  figure  the  H2O  seems  to  be  chemically  combined  with  the 
H2SO4  and  no  water  vapor  exists.  SO3  coming  in  contact  with 
water  vapor  forms  very  small  drops  of  sulphuric  acid,  almost 
impossible  to  condense,  and  any  S03  used  in  this  way  may  be 
considered  as  lost  beyond  any  reasonable  hope  of  recovery,  as 
even  a  very  long  condensation  and  absorbtion  apparatus  will 
catch  very  little  of  it. 

The  second  vapor,  that  of  S03,  is  only  met  with  in  making 
fuming  acid.  A  glance  at  the  absorbtion  curve  will  show  how 
rapidly  the  absorbtion  drops,  as  the  strength  of  the  absorbing 
acid  increases.  But  SO3  passing  through  fuming  acid  unab- 
sorbed  is  in  no  way  changed,  and  is  caught  perfectly  by  the 
close  to  100  per  cent  acid  in  the  back  of  the  system. 

The  vapor  pressure  of  foreign  acids  comes  of  course  from 
impure  materials.  Sometimes  it  is  necessary  to  clean  out  the 
system  after  foreign  acids  have  gotten  in;  but  frequently  any 
trouble  of  this  character  can  be  cured  by  letting  the  system  get 
as  hot  as  possible  and  simply  "boiling  out"  the  foreign  substance. 
It  is  necessary  to  watch  weak  acid  from  chamber  plants  closely, 
to  prevent  nitric  acid  getting  in. 


ELEMENTARY  CHEMISTRY  OF  SULPHURIC  ACID         15 

As  fuming  acid  has  high  melting  points,  the  exact  varying  with 
the  strength,  the  temperature  must  be  kept  up  sufficiently  high 
to  prevent  freezing.  In  shipping  fuming  acid  it  is  general 
practice  to  add  a  little  nitric,  if  the  intended  use  will  not  be 
interfered  with  by  nitric  acid.  Five  per  cent  of  nitric  acid  will 
drop  the  freezing  point  of  fuming  acid  to  —  10.5°F. 


CHAPTER  III 
CHARACTERISTICS  AND  USES 

Sulphuric  acid  is  a  viscous,  colorless  (when  pure)  liquid, 
composed,  by  weight,  of  2.04  per  cent  hydrogen,  32.64  per  cent 
sulphur,  and  65.28  per  cent  oxygen.  It  is  very  strongly  acid. 

Its  most  outstanding  characteristic  is  its  affinity  for  water, 
either  free  or  combined,  and  violent  combination,  with  evolution 
of  much  heat,  with  it. 

The  sulphuric  acid  industry  is  a  business  barometer,  as  the 
acid  enters  into  most  other  industries,  and  general  trade  condi- 
tions are  very  soon  reflected  in  both  sales  and  prices. 

Sulphuric  acid  forms  sulphates  with  all  the  metals,  replacing 
any  other  acid  radical,  and  freeing  the  other  acid.  Its  affinity 
for  water  makes  it  the  most  important  desiccating  agent  known. 
It  readily  forms  bisulphates  (acid  sulphates)  and  double  sul- 
phates. Most  of  its  combinations  are  characterized  by  extreme 
stability.  Below  65  per  cent  H2S04  it  attacks  iron  vigorously; 
above  that,  very  little.  Below  92  per  cent  H2S04  its  action 
upon  lead  is  slight — it  increases  fast  with  strength.  Hot  acid 
acts  more  vigorously  than  cold.  The  water  in  sulphuric  acid 
of  98.3  per  cent  concentration  seems  to  be,  not  a  diluent,  but  an 
actual  part  of  the  acid,  exerting  none  of  the  characteristics  of 
water  in  the  less  high  concentrations. 

Upon  these  main  characteristics  depends  the  important  place 
of  sulphuric  acid  in  modern  life.  A  list  of  the  industries  using 
it  would  be  a  catalogue  of  the  industry  of  the  world. 

The  LeBlanc  process  for  soda  ash,  dating  from  the  end  of  the 
eighteenth  century,  took  the  manufacture  of  sulphuric  acid  out 
of  the  drug  business,  and  made  it  a  major  industry. 

Common  salt,  treated  with  sulphuric  acid,  gives  off  hydrochloric 
acid,  with  the  formation  of  sodium  sulphate,  after  the  formula 
2NaCl  +  H2S04  =  2HC1  +  Na2S04 

The  sodium  sulphate,  roasted  with  coal  and  slaked  lime,  gives 
soda  ash  (sodium  carbonate),  oxide  and  sulphide  of  calcium,  and 
carbon  dioxide. 

There  are  other  methods  of  making  sodium  carbonate  from  the 
sulphate,  with  by-products  of  sulphur  and  hyposulphites,  but 
the  LeBlanc  process  is  still  a  tremendous  producer. 

Nitric  acid  is  made  from  its  natural  sodium  salt,  Chile  saltpeter, 

16 


CHARACTERISTICS  AND  USES  17 

by  treatment  with  sulphuric  acid,  the  result  being  nitric  acid  and 
sodium  sulphate,  or  salt  cake.  By  the  use  of  twice  the  theoretical 
amount  of  sulphuric  acid  a  bisulphite  is  formed,  which  is  fusible, 
and  easily  removed  from  the  stills.  This  bi-,  or  acid,  sulphate, 
has  many  of  the  characteristics  of  the  acid  itself,  and  is  fre- 
quently used  for  pickling  iron  castings,  its  31  per  cent  of  free 
H2SO4  being  sufficient  to  accomplish  this  purpose. 

Petroleum  refining  consumes  large  quantities  of  sulphuric  acid. 

Without  sulphuric  acid  and  its  product,  nitric  acid,  the  coal  tar 
dye  industry  could  not  exist. 

The  fertilizer  industry  depends  upon  sulphuric  acid  for  its 
sulphate  of  lime,  or  land  plaster;  and  even  more,  as  a  means  of 
converting  cheap  phosphate  rock  into  a  soluble  form,  from  which 
phosphoric  acid  is  made. 

The  medical  profession  uses  it  in  many  ways.  The  quinine  we 
are  brought  up  on  is  the  sulphate  of  that  alkaloid.  The  manu- 
facture of  " sulphuric"  ether  from  ethel  alcohol  uses  sulphuric 
acid  as  a  catalytic  agent. 

In  all  nitrating  processes,  whether  for  celluloid,  nitro-cellulose, 
either  for  ammunition  or  some  form  of  soluble  cotton,  the  action 
of  sulphuric  is  a  desiccating  one,  removing,  and  holding  fast  to 
the  OH  radical  released,  preventing  its  doing  any  harm. 

Fuming  Sulphuric  Acid  is  a  solution  of  SO  3  in  H2SO4 — it  is 
largely  used  in  the  manufacture  of  coal  tar  dye  stuffs.  Its  most 
important  use  is  the  "butting  up"  the  96  per  cent  to  97.5  per 
cent  acid  of  the  best  concentrators  to  the  100  per  cent  that  is 
needed  in  many  industries. 

The  popularity  of  the  sulphate  method  of  pulping  wood  is 
growing,  and  with  it  the  use  of  H2SO4.  It  is  not  necessary  to 
pick  the  wood  so  carefully,  as  in  the  sulphite  or  caustic  methods, 
as  resinous  parts,  such  as  knots  or  sappy  wood,  are  pulped  by 
it  to  an  extent  impossible  by  any  other  method. 

An  extensive  use  for  sulphuric  acid  is  (was)  in  the  preparation 
of  the  mash  for  distilling. 

The  large  number  of  alums,  used  especially  in  the  textile 
industry,  are  double  sulphates.  Originally  sulphate  of  alumina 
was  invariably  one  of  the  sulphates,  chromium,  iron,  sodium, 
potassium  and  ammonium  being  the  usual  others,  and  from  the 
aluminum  it  took  its  name-^but  today  other  pairs  of  sulphates 
go  under  the  name  of  alum.  Sulphate  of  alumina,  free  from 
iron,  is  used  as  a  mordant  and  dyeing  agent,  to  escape  the  injurious 
iron  that  alum  frequently  carries. 


18 


AMERICAN  SULPHURIC  ACID  PRACTICE 


Both  alum  and  sulphate  of  alumina  have  wide  application  for 
clarifying  drinking  water,  and  in  coagulating  and  settling  sewage. 

Sulphate  of  zinc  is  used  as  a  drier  for  paints,  a  disinfectant,  and 
a  mordant  in  dyeing. 

Much  of  the  electroplating  industry,  including  the  electrolytic 
refining  of  copper  and  other  metals,  uses  the  suphate  of  the  metal 
as  the  electrolyte. 

Copper  sulphate,  or  blue  vitriol,  and  iron  sulphate,  or  green  vit- 
riol, have  large  application  in  the  dyeing  industry,  also  in  recovering 
silver  by  the  amalgamation  process.  Green  vitriol,  perhaps  better 
known  as  copperas,  is  very  largely  used  in  ink  manufacturing. 

The  leaching  of  low  grade  copper  ores-with  weak  solutions  of  sul- 
phuric acid  has  become  a  great  industry  within  the  last  few  years. 

"Shoddy"  wool  is  freed  from  cotton  by  " carbonizing "  the 
goods  with  sulphuric  acid,  which  consists  in  letting  a  solution  of 
acid  dry  on,  when  the  cotton  or  other  vegetable  fibre  gives  up  its 
OH  radicalj  only  the  carbon  remaining,  and  that  in  the  form  of  a 
powder,  which  is  easily  shaken  off. 

The  foregoing  is  only  a  brief  list  of  some  of  the  most  important 
uses  to  which  sulphuric  acid  may  be  put,  and  is  not  intended  to 
do  more  than  show  how  dependent  modern  civilization  is  upon 
this  industry. 

The  Bureau  of  Mines  Bulletin  No.  184  reports  for  the  period 
June  to  August,  1918,  the  following  distribution  of  sulphuric 
acid  among  the  industries: 

TABLE  2 


Industry 

Tons  acid  used 
per  month.  On 
basis  of  100  per 
cent  H2SO4 

Tons  per  year. 
50°Be.  basis 

Per  cent  of 
total  acid 
uaed 

1.  Explosives  (military  and  domestic).  . 
2.  Fertilizers 

140,000 

111  000 

2,700,000 
2  130  000 

36.0 

28  0 

3.  Oil  refineries  .      .    . 

35,000 

671,000 

8  8 

4.  Chemicals,   drugs,   and  ammonium 
sulphate  

38,500 

740,000 

9  9 

5.  Steel  pickling  and  galvanizing  
6.  Fabrics  textiles  etc 

36,500 
5  200 

700,000 
100  000 

9.3 
1  3 

7.  Paints,  lithophone,  glue,  etc  

5,300 

104,000 

1.4 

8.  Metallurgical,  including  storage  bat- 
teries 

15,200 

292  ,  000 

3  9 

9.  Miscellaneous  

3,800 

73,000 

1.0 

Total                                    

390,500 

7,510,000 

100  0 

CHARACTERISTICS  AND  USES 


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Tiltonville,  Ohio, 
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St.  Bernard,  Ohio 

Sandusky,  Ohio 
Bradford,  Pa. 
Beaver  Falls,  Pa. 

Donora,  Pa. 
Erie,  Pa. 
Langeloth,  Pa. 

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Jarecki  Chemical  Co.  .  . 
Virginia-Carolina  Chem 
Farmers'  Fertilizer  Co.  . 
Smith  Agricultural  Chei 

Grasselli  Chemical  Co.  . 

Grasselli  Chemical  Co.  . 
New  Jersey  Zinc  Co  

St.  Bernard  Acid  Workg 

Virginia-Carolina  Chem 
American  Alkali  &  Acid 
Grasselli  Chemical  Co.  . 

American  Steel  &  Wire 
Donora  Zinc  Works  .... 
F.  H.  Kalbfkeisch  Corp 
American  Zinc  &  Chemi 

Pennsylvania  Salt  Manx: 
Co. 
Grasselli  Chemical  Co  .  . 

General  Chemical  Co.  .  . 
American  Sheet  Tin  &  P! 
Riverside  Acid  Works.  . 

Fairmount  Chemical  Cc 

United  Zinc  Smelting  C 

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28  AMERICAN  SULPHURIC  ACID  PRACTICE 

This  table  shows,  eliminating  the  acid  used  for  munitions  and 
explosives,  and  allowing  about  10,000  tons  per  month  for  domestic 
explosives,  an  indicated  requirement  for  normal  peace  purposes 
of  possibly  260,000  tons  per  month  (basis,  100  per  cent  H2SC>4), 
or  about  5,000,000  tons  per  year  (basis,  50°Be.). 

There  is  no  question  that  the  use  of  phosphate  fertilizer  will 
increase  all  over  the  country  for  many  years.  And  as  acid  is 
expensive  to  transport,  it  will  have  to  be  made  near  the  place  it 
is  used. 

Sulphur,  the  primary  raw  material,  either  as  pyrites  or  brim- 
stone has  recently  been  described  by  Drs.  Raymond  F.  Bacon 
and  Harold  S.  Davis  before  the  American  Institute  of  Chemical 
Engineers.  The  following  extracts  have  been  taken  from  their 
paper.1 

America  now  dominates  the  sulphur  industry  and  virtually  all  the 
American  sulphur  is  produced  by  three  companies — viz.,  the  Union 
Sulphur  Co.,  the  Freeport  Sulphur  Co.  and  the  Texas  Gulf  Sulphur  Co. 
These  three  companies  produce  not  only  virtually  all  the  sulphur  used 
in  the  United  States  but  also  a  considerable  surplus  which  is  exported. 
The  only  other  sulphur  which  normally  enters  the  American  market  in 
quantity  comes  from  Japan  and  its  percentage  calculated  on  the  con- 
sumption of  the  United  States  is  small  and  is  not  likely  to  increase. 
Rising  costs  of  living  have  meant  much  higher  wages  in  Japan,  as  well 
as  in  other  parts  of  the  world;  in  fact,  the  percentage  increase  has  prob- 
ably been  greatest  in  Japan,  due  not  only  to  world  conditions  affecting  all 
countries  but  to  the  rising  standards  of  living  of  the  Japanese.  These 
facts,  together  with  present  higher  transportation  costs,  will  make  it 
increasingly  difficult  for  Japanese  sulphur  to  compete  on  our  Pacific 
coast  with  the  American  product. 

EXPANSION  OF  INDUSTRY  DURING  WAR 

During  the  World  War,  and  especially  after  America's  entry  into  it, 
the  demand  for  sulphur  grew  enormously.  Some  time  previous  to  our 
declaration  of  war  consideration  had  been  given  by  a  certain  group  of 
New  York  capitalists  to  the  opening  up  of  the  sulphur  deposit  (known 
as  the  "Big  Dome")  located  near  Matagorda,  Tex.  These  plans  were 
hastened  to  realization  by  our  Government's  need  and  demand  during 
the  war  for  the  maximum  production  from  every  possible  source  of  sul- 
phur. The  plans  eventuated  in  the  formation  of  the  Texas  Gulf  Sul- 
phur Co.,  which,  however,  did  not  get  its  plants  into  operation  until 
after  the  armistice.  Production  has  been  practically  continuous  since 

Chem.  &  Met.  Eng.,  January  12,  1921. 


CHARACTERISTICS  AND  USES 


29 


FIG.  1.— Views  of  the  Texas  Gulf  Sulphur  Co. 
General  Views  Showing  Topography,  Figs.  1,  2,  5,  8. 
Sulphur  Tank  Storage  System,  Figs.  3,  6,  9. 
Well  Driving  Equipment,  Figs.  4,  7,  10. 


30 


AMERICAN  SULPHURIC  ACID  PRACTICE 


FIG.  2. — Views  of  the  Texas  Gulf  Sulphur  Co. 
Houses,  Pavilion  and  Hospital,  Figs.  11,  14,  17,  20. 
Method  of  Loading  for  Shipment,  Figs.  12,  15,  18. 
Exterior  and  Interior  Views  of  Power  House,  Figs.  13,  16,  19. 


CHARACTERISTICS  AND  USES  31 

the  company  first  mined  sulphur  on  March  19,  1919.  The  plant  of 
this  company,  which  has  been  described  elsewhere,1  was  designed  to 
have  a  capacity  of  1,000  tons  of  sulphur  per  day,  but  for  months  at  a 
time  during  the  past  year  it  has  produced  on  an  average  2,000  tons  per 
day.  The  total  production  for  the  year  1920  exceeds  800,000  long  tons, 
while  in  all  probability  the  production  for  1921  will  be  the  largest  of 
any  sulphur  company  in  the  world.  The  possible  daily  production 
with  the  present  plant,  under  favorable  conditions,  could  be  forced  to 
3,000  or  4,000  tons  per  day.  The  deposit  contains  upward  of  ten 
million  tons  of  sulphur;  and  a  brief  description  of  its  character  is  as 
follows: 

DESCRIPTION  OF  BIG  DOME  AT  MATAGORDA 

The  main  deposit  has  a  diameter  of  about  4,000  ft.  and  is  situated 
800  to  1,000  ft.  below  the  surface  of  the  ground.  The  sulphur  occurs 
in  an  almost  flat  stratum,  whose  general  shape  is  like  that  of  a  flat- 
topped  umbrella.  Above  the  sulphur  stratum  is  an  unconsolidated 
sediment  consisting  of  bands  of  shale,  gumbo  and  boulders.  Below  is 
a  layer  of  salt  and  gypsum,  and  then  a  layer  of  salt  of  undetermined 
but  very  considerable  thickness.  The  sulphur  content  of  the  deposit 
runs  quite  uniform  with  a  slightly  higher  percentage  of  sulphur  on  one 
side  of  the  dome.  The  mining  operations  are  carefully  checked,  and  a 
large-sized  model  of  the  deposit  enables  the  engineers  constantly  to 
visualize  what  is  taking  place  underground. 

PRODUCTION  AND  STOCKS  EXCEED  POST-WAR  NORMAL  DEMAND 

At  the  time  the  Texas  Gulf  Sulphur  Co.  entered  the  market  the  situa- 
tion was  about  as  follows:  The  Union  Sulphur  Co.  had  on  top  of  the 
ground,  in  unsold  stock  of  sulphur,  upward  of  one  million  tons  and  the 
Freeport  Sulphur  Co.  had  several  hundred  thousand  tons.  The  normal 
consumption  of  sulphur  in  the  United  States  had  been  between  four  and 
five  hundred  thousand  tons  per  annum,  which  quantity  could  be  readily 
supplied  by  the  two  older  companies.2  A  new  sulphur  company  enter- 
ing the  market  with  a  large  production  of  sulphur  was  therefore  com- 
pelled to  pursue  one  of  two  policies — either  to  attempt  to  obtain  a  share 

Read  before  the  American  Institute  of  Chemical  Engineers,  New  Orleans, 
December  6,  1920.  By  RAYMOND  F.  BACON  and  HAROLD  S.  DAVIS. 

1  Chem.  &•  Met.  Eng.,  vol.  20,  No.  4,  pp.  186-188.     Eng.  Min.  J.,  vol.  107 
(1919),  pp.  555-557. 

2  It  may  be  stated,  in  passing,  that  any  economic  data  given  regarding 
either  the  Union  Sulphur  Co.  or  the  Freeport  Sulphur  Co.  are  subject  to 
the  usual  statement  on  advertisements  of  bond  sales;  that  is,  "they  are 
gathered  from  sources  we  believe  to  be  reliable,  but  are  not  guaranteed  by 
us." 


32  AMERICAN  SULPHURIC  ACID  PRACTICE 

of  the  business  by  cutting  prices  or  to  place  the  sulphur  in  markets 
which  had  not  hitherto  used  sulphur;  in  other  words,  to  increase  the 
sulphur  consumption  of  the  country. 

With  reference  to  the  first  possibility,  competition  based  on  cut- 
throat slashing  of  prices  always  has  proved  disastrous  to  the  whole 
industry.  Moreover,  the  mining  of  sulphur  by  the  Frasch  process,  to 
be  carried  out  economically,  must  be  conducted  on  a  very  large  scale, 
so  that  even  if  a  company  under  the  conditions  outlined  above  had 
obtained  a  third  of  a  possible  500,000-ton  consumption,  this  would  not 
have  insured  profitable  operation.  The  company  has  chosen  what  is 
surely  the  wiser  course,  in  attempting  to  place  its  sulphur  by  increasing 
the  total  consumption  in  the  industries. 

It  was  possible  to  do  this  owing  to  the  prevailing  economic  conditions. 
The  United  States  had  in  recent  years  consumed  annually,  for  the  manu- 
facture of  sulphuric  acid,  upward  of  500,000  tons  of  sulphur  in  the  form 
of  pyrites,  most  of  which  came  from  Spain.  The  older  sulphur  com- 
panies, either  because  of  some  agreement  with  the  pyrites  importers  or 
because  of  a  desire  to  hold  the  price  of  sulphur  at  a  certain  level,  had 
not  attempted  seriously  in  past  years  to  substitute  sulphur  for  pyrites 
as  the  raw  material  of  sulphuric  acid  manufacture.  Importation  of 
Spanish  pyrites,  due  "to  war  transportation  conditions,  fell  off  very 
seriously  during  the  war  years.  This  caused  many  producers  of  sul- 
phuric acid  to  discard  the  pyrites  roasters  and  to  install  sulphur-burning 
equipment,  while  new  producers  in  this  field  erected  plants  which  were 
almost  entirely  so  equipped.  The  new  company  was  able  to  obtain  its 
fair  proportion  of  the  new  business  and  the  net  result  has  been  that 
the  total  consumption  of  sulphur  of  the  United  States  during  the  past 
year  has  been  upward  of  1,000,000  tons,  as  compared  with  a  normal 
consumption  in  recent  years  of  about  half  that  figure. 

PYRITES  VERSUS  SULPHUR  AS  A  SOURCE  OF  S02 

It  is  interesting,  in  this  connection,  to  give  just  a  little  history,  for  if 
the  subject  is  examined  it  is  found  that  in  the  early  days  of  sulphuric 
acid  manufacture  all  the  sulphuric  acid  of  Europe,  excepting  Nord- 
hausen  acid,  was  made  from  brimstone.  This  includes  the  period  from 
about  1750  to  1839,  when  pyrites  first  was  used  commercially  for  the 
manufacture  of  sulphuric  acid  in  England.  This  use  of  pyrites  was 
due  to  the  fact  that  the  Neapolitan  Government  in  1838  granted  a 
monopoly  for  the  exportation  of  sulphur  to  Taix  &  Co.,  of  Marseilles, 
which  firm  immediately  raised  the  price  of  sulphur  from  $25  to  $70  per 
ton.  By  so  doing,  it  killed  the  goose  that  laid  the  golden  egg,  for 
pyrites  was  substituted  immediately  for  sulphur  in  most  European 
countries  and  the  era  of  high-priced  sulphur  was  but  short  lived.  The 
loss  of  this  market  was  a  permanent  setback  to  Sicilian  sulphur. 


CHARACTERISTICS  AND  USES  33 

-  The  subsequent  history  of  the  sulphur  industry  is  one  of  violent  ups 
and  downs.  If  one  considers  this  history  up  until  some  time  after 
Frasch  made  America  a  factor  in  the  business,  it  will  be  noted  that  it 
has  been  characterized  at  all  times  by  short  periods  of  prosperity, 
followed  by  a  short-sighted,  selfish,  destructive  competition  on  the  part 
of  certain  interests.  Following  this  would  come  a  period  of  such  marked 
depression  as  to  threaten  the  life  of  the  entire  industry,  and  it  would 
be  necessary  for  some  governmental  or  other  outside  agency  to  exercise 
pressure  to  get  the  producers  together  on  a  common-sense  basis  and 
thus  gradually  put  the  industry  again  on  its  feet.1  Since  the  time  when 
Frasch  made  possible  America's  sulphur  industry  the  stability  of  the 
whole  industry  has  been  much  greater.  While  at  the  present  time  there 
is  an  extremely  lively  competition  among  the  companies  for  business, 
there  is  every  reason  to  believe  that  American  common  sense,  spirit  of 
fair  play,  and  co-operation  will  prevent  this  competition  going  to  the 
extent  of  threatening  the  industry  itself,  as  has  happened  many  times 
in  the  past.  Present  indications  are  that  all  the  sulphur  companies  are 
pursuing  an  enlightened  policy,  in  that  all  are  doing  more  or  less  research 
and  development  work  having  as  its  ultimate  object  the  opening  up  of 
broader  markets  for  sulphur,  of  which  sulphuric  acid  manufacture 
affords  but  one. 

ADVANTAGES  OF  SULPHUR  OVER  PYRITES 

For  sulphuric  acid  manufacture  sulphur  has  many  very  marked  ad- 
vantages over  pyrites.  Using  pyrites  means  handling  into  the  works  a 
comparatively  large  quantity  of  material,  its  slow  combustion  in  expen- 
sive roasters,  a  certain  inevitable  dust  nuisance  and  the  disposal  of  a 
large  tonnage  of  cinder.  As  against  this,  sulphur  of  less  than  one-half 
the  weight  of  pyrites  for  a  given  tonnage  of  acid  produced  is  handled 
into  the  works,  is  burned  cleanly  in  inexpensive  equipment  and  leaves 
no  residues  to  be  taken  care  of.  Sulphur  is  constant  in  composition, 
and  its  freedom  from  arsenic  and  other  impurities  allows  the  production 
of  a  purer  acid.  It  is  also  claimed  that,  in  practice,  the  burning  of 
sulphur  means  a  higher  rate  of  production  for  a  given  size  of  lead  cham- 
ber space. 

These  acknowledged  advantages  of  the  use  of  sulphur  over  pyrites 
for  sulphuric-acid  manufacture  have  been  demonstrated  by  the  willing- 
ness of  acid  producers  to  pay  a  higher  price  per  unit  for  elementary 
sulphur  than  for  combined  sulphur  in  the  form  of  pyrites.  An  example 
of  this  is  the  fact  that  one  of  our  largest  and  best  organized  chemical 
companies,  in  making  a  large  contract,  chose  sulphur  over  pyrites  for 
sulphuric  acid  manufacture,  where  the  differential  in  offered  prices  was 
8c.  per  unit  of  sulphur. 

1  In  this  connection,  see  FRASCH,  Perkin  Medal  Address,  Met.  &•  Chem. 
Eng.,  vol.  10,  No.  2,  pp.  73-82,  and  J.  Ind.  Eng.  Chem.,  vol.  4  (1912),  p.  139. 


34  AMERICAN  SULPHURIC  ACID  PRACTICE 

When  one  considers  the  present  high  prices  of  labor,  the  uncertainty 
of  the  copper  market  and  the  fact  that  sulphur  may  be  purchased  in  a 
competing  market,  from  concerns  which  have  large  stocks  on  hand,  so 
that  delivery  is  certain,  it  would  seem  to  be  a  wise  business  policy  to 
use  sulphur  rather  than  pyrites  for  sulphuric  acid  manufacture  even 
with  a  very  large  differential  in  price.  This  is  especially  true  when  one 
considers  the  other  side  of  the  situation — namely,  that  in  buying  im- 
ported pyrites  the  consumer  is  putting  himself  at  the  mercy  of  one  large 
set  of  interests  which,  while  it  may  at  the  present  time  offer  pyrites  at 
low  prices  and  even  below  actual  cost,  will  almost  certainly  at  some  time 
in  the  future  reap  its  profit  by  much  higher  prices.  It  is  said  that 
imported  pyrites  has  been  offered  for  large  contracts  in  this  country  at 
about  lOc.  per  unit  of  sulphur,  ex-vessel,  Atlantic  seaboard,  while  at  the 
same  time  pyrites  was  selling  in  England,  much  nearer  the  base  of 
supplies,  at  20c.  to  22c.  per  unit  of  sulphur.  It  reminds  one  somewhat 
of  the  tactics  of  Standard  Oil  in  the  old  days  before  "  trust-busting " 
became  fashionable  with  politicians;  and  everyone  knows  that  those 
who  bought  cheaply  when  the  company  was  extinguishing  a  competitor 
never  reaped  any  permanent  advantage,  but  later  more  than  paid  for 
temporary  reductions  in  price. 

Sulphur  is  today  one  of  the  few  substances  which  have  not  risen  in 
price  since  pre-war  days.  In  fact,  sulphur  is  cheaper  today  than  at  any 
other  time  in  the  history  of  the  industry.  The  price  for  large  contracts 
is  about  $20  per  ton,  Atlantic  seaboard.  This  makes  sulphur  one  of 
the  cheapest  raw  materials  available  and  should,  it  would  seem,  greatly 
extend  its  usefulness.  Sulphur  as  mined  and  sold  by  all  three  com- 
panies is  of  remarkably  high  grade.  In  fact,  many  so-called  C.P.  chem- 
icals do  not  possess  the  purity  of  crude  sulphur,  as  sold  by  these 
companies.  The  sulphur  is  free  from  arsenic,  selenium  and  tellurium, 
and  of  ten  for  days  at  a  time  wells  will  yield  a  product  running  higher  than 
99.9  per  cent  sulphur,  as  calculated  on  a  moisture-free  basis;  in  fact, 
sulphur  companies  selling  the  crude  sulphur  on  contracts  guarantee  the 
purity  to  be  over  99  or  99^  per  cent. 

EFFECT  OF  TRACES  OF  PETROLEUM  ON  COMBUSTION 

One  impurity  occurring  in  traces  in  the  sulphur  of  all  three  companies 
is  oil.  There  is  a  dearth  of  information  in  the  technical  literature 
respecting  the  subject  of  oil  in  sulphur.  Since  the  effect  of  this  im- 
purity is  very  interesting,  it  is  appropriate  to  discuss  it  here.  The 
peculiar  effect  of  oil  is  its  influence  on  the  burning  qualities  and  also  on 
the  color  and  odor  of  sulphur.  A  priori,  one  would  not  assume  that 
mere  traces  of  a  combustible  substance  like  petroleum  oil  could  affect 
adversely  the  combustion  of  another  combustible  substance  like  sulphur, 
but  such  is  indeed  the  case. 


CHARACTERISTICS  AND  USES  35 

If  one  will  make  a  simple  experiment  by  attempting  to  burn  two  small 
lots  of  sulphur,  one  being  chemically  pure  and  the  other  containing  0.2 
per  cent  of  petroleum  oil,  he  will  note  the  following  phenomena:  The 
pure  sulphur  will  burn  quietly  until  it  is  totally  consumed;  the  sulphur 
containing  the  oil  will  burn  for  a  very  short  time,  when  it  will  be  ob- 
served that  a  thin,  elastic  film  is  being  formed  over  its  surface.  Very 
soon  combustion  is  taking  place  only  in  spots,  and  within  an  exceedingly 
short  time  the  flame  goes  out,  although  only  a  small  percentage  of  the 
sulphur  has  been  consumed.  The  explanation  is  quite  simple.  Sulphur 
and  oil  at  a  moderate  temperature  react  together  to  form  asphalt,  and 
if  the  reaction  is  carried  to  completion  the  final  result  is  carbon. 

In  the  burning  of  sulphur  containing  oil  the  oil  reacts  with  the  sulphur 
to  form  an  asphaltic  material,  which  quickly  spreads  as  a  film  over  the 
surface.  The  result,  as  combustion  proceeds,  is  a  film  of  carbon  over 
the  surface  of  the  sulphur.  The  ignition  temperature  of  carbon,  or  of 
the  intermediate  asphaltic  material,  is  so  much  highej  than  that  of 
sulphur  itself  or  than  the  temperature  developed  during  the  burning 
of  the  sulphur  that  this  film  is  not  ignited  and  consequently  the  whole 
flame  is  extinguished. 

The  remedy  for  burning  such  sulphur  is  also  quite  obvious.  If  the 
devices  for  sulphur  combustion  are  such  as  to  agitate  the  surface  of  the 
burning  sulphur  or  in  any  other  way  break  this  film  of  asphaltic  mate- 
rial, no  difficulty  will  be  experienced.  Acid  manufacturers  who  use 
mostly  modern  types  of  sulphur  burners,  such  as  the  rotary  or  cascade 
type,  which  allow  the  sulphur  to  drop  from  one  level  to  another,  have 
absolutely  no  difficulty  in  burning  sulphur  containing  0.2  per  cent  of 
oil,  which  figure  represents  more  oil  than  any  of  the  commercial  sul- 
phurs contain  at  the  present  time.  On  the  other  hand,  many  of  the 
small  paper-pulp  manufacturers  still  adhere  to  types  of  burners  in 
which  the  burning  sulphur  is  more  or  less  quiescent.  With  such  a  type 
there  is  no  agitation  of  the  burning  liquid  surface,  so  that  some  of  these 
paper-pulp  manufacturers  have  had  difficulty  in  burning  sulphur  when 
they  happened  to  obtain  a  shipment  comparatively  high  in  oil. 

The  sulphur  deposits  of  all  three  operating  companies  are  located  in 
close  proximity  to  oil  fields.  When  a  sulphur  deposit  is  first  opened 
some  of  the  product  may  be  high  in  oil,  running  as  much  as  0.2  per  cent, 
but  as  production  proceeds  the  oil  becomes  progressively  lower  until 
finally,  for  days  at  a  time,  it  may  amount  to  only  0.04  per  cent,  which  is 
totally  negligible,  even  for  burners  which  provide  no  agitation  of  the 
surface.  We  have  assumed  that  hot  water  carried  this  small  quantity 
of  oil  from  small  crevices  in  the  oil-sand  formation  to  the  sulphur  below 
when  the  well  was  first  opened.  After  a  region  has  become  heated  up 
by  the  hot  water,  these  traces  of  oil  are  pretty  well  washed  out;  conse- 
quently, sulphur  mined  later  in  the  same  area  is  virtually  free  from  it. 
Examination  of  drill  cores  of  native  sulphur  showed  such  in  situ  sul- 


36  AMERICAN  SULPHURIC  ACID  PRACTICE 

phur  to  be  oil-free.  We  are  informed  by  ex-employees  of  the  Union 
Sulphur  Co.  that  this  corresponds  with  the  experiences  of  that  organ- 
ization in  heating  up  any  new  area  of  sulphur  ground.  The  examina- 
tion of  a  very  large  number  of  samples  of  sulphur,  representing  the 
production  of  all  three  companies,  has  shown  quite  positively  that  none 
of  their  sulphur  contains  enough  oil  to  cause  any  difficulty  in  its  com- 
bustion with  rotary  burners  or  other  burners  which  agitate  the  surface  of 
the  burning  sulphur  during  combustion.  It  is  only  very  exceptionally 
that  one  will  find  a  car  of  sulphur  whose  oil  content  is  high  enough  to 
make  difficulties  in  its  combustion  in  a  stationary  type  of  burner. 

PROPERTIES  AND  USES  OF  SULPHUR 

Sulphur  is  now  and  is  likely  to  be  for  some  time  one  of  our  cheapest 
raw  materials,  and  accordingly  should  and  undoubtedly  will  find  a 
much  wider  range  of  usefulness.  It  is  by  studying  the  physical  and 
chemical  properties  of  a  substance  that  one  first  obtains  ideas  as  to 
possible  new  uses  therefor.  The  chief  physical  properties  of  sulphur 
are  tabulated  in  Table  4.  The  present  tonnage  uses  of  sulphur  are 
presented  in  the  chart.  Those  properties  which  suggest  certain  possible 
tonnage  uses  for  sulphur  are  its  very  poor  conductivity  of  heat  and 
electricity,  its  resistance  to  being  wetted  by  water  and  its  inertness 
toward  most  acids,  all  of  this  combined  with  a  fair  degree  of  physical 
strength.  These  properties  suggest  heat-insulating  materials,  electrical 
insulators  of  various  types,  water-  and  acid-proof  cements,  and  acid- 
proof  construction  materials. 

As  against  the  properties  of  sulphur  which  might  make  it  very  desir- 
able for  certain  construction  purposes  are  certain  objectionable  ones, 
such  as  its  brittleness  and  its  flammability.  The  brittleness  can  be 
overcome  sufficiently  for  many  purposes  by  making  mixtures  of  sulphur 
with  other  materials,  such  as  sand,  asbestos,  or  paper  pulp,  or  by  rein- 
forcing with  wire  screen.  In  many  cases  the  flammability  is  not  a 
serious  objection. 

A  survey  of  the  literature,  especially  the  patents,  on  the  subject  of 
sulphur  mixtures  reveals  that  almost  every  conceivable  thing  has  been 
suggested  as  a  perfective  admixture  for  sulphur  to  obtain  a  material 
which  has  all  the  air-  and  acid-resistant  properties  one  could  desire  or 
to  get  a  completely  resistant  kind  of  concrete  useful  in  building.  We 
have  tested  out  most  of  the  recipes  which  appeared  to  be  promising  and 
find  as  usual  that  the  claims  have  been  much  overstated.  However, 
the  ordinary  mixture  of  sand  and  sulphur  which  has  been  repeatedly 
mentioned  in  the  literature  has  merits  which  should  make  it  better 
known.  The  mixture  which  has  seemed  to  us  the  best  for  most  uses  is 
that  of  40  of  sulphur  and  60  of  sand  (parts  by  weight).  The  tensile 
strengths  of  sulphur-sand  mixtures  as  measured  in  the  usual  manner  for 
testing  cement  were  as  follows: 


CHARACTERISTICS  AND  USES  37 

TABLE  3. — TENSILE  STRENGTHS  OF  SULPHUR-SAND  MIXTURES 

PERCENTAGE  OF  SULPHUR  TENSILE  STRENGTH, 

BY  WEIGHT  LB.  PER  SQ.   IN. 

25  90 

35  310 

40  400 

45  310 

50  110 

100  250 

We  have  also  used  other  fillers  which  have  given  tensile  strengths  of 
800  and  even  1,100  Ib.  measured  in  the  same  manner  and  have  to  a 
large  extent  overcome  the  brittleness  of  the  sulphur  in  some  of  these 
mixtures.  Sulphur-sand  briquets  kept  on  hand  for  one  year  show  no 
deterioration  in  strength.  It  is  evident  that  the  40:60  sulphur-sand 
mixture  can  be  used  as  an  acid-resistant  concrete,  for  making  acid- 
resisting  pipe,  tanks,  gutters,  launders,  etc.  The  manipulation  of  such 
a  mixture  is  much  like  that  of  pouring  concrete  and  is  as  follows: 

Practical  Manipulation. — It  is  evident  that  the  sand  should  contain 
no  constituent  which  will  be  attacked  by  any  material  which  is  to  come 
in  contact  with  the  finished  product;  for  instance,  in  the  case  of  acid 
tanks  it  should  be  free  from  limestone  or  other  acid-soluble  constituents. 
If  necessary,  it  should  be  washed  and  dried.  The  sulphur  may  be 
melted  in  a  kettle  with  constant  stirring,  and  the  sand,  which  has  been 
heated  separately,  poured  into  it  while  the  stirring  is  continued.  Un- 
less the  sand  is  heated,  it  will  lump  when  poured  into  the  sulphur. 
When  the  material  is  thick  enough  (40  per  cent  sulphur  and  60  per  cent 
sand)  it  is  ladled  into  the  molds. 

Considerable  flexibility  is  possible  in  handling  this  material.  For 
instance,  a  small  tank  was  made  which  was  2  ft.  square,  18  in.  deep, 
and  2  in.  thick.  The  mixture  was  poured  into  a  wooden  mold  in  twelve 
different  lots.  Although  several  of  these  lots  had  solidified  before  the 
next  was  poured  upon  them,  nevertheless  the  resulting  joints  were 
strong.  Apparently  the  hot  mixture  melts  sufficient  of  the  solidified 
part  to  form  a  solid  joint.  There  was  no  contraction  of  the  tank  as  a 
whole  and  no  tendency  to  split  in  the  mold.  This  mixture  can  be 
worked  with  a  trowel,  like  mortar.  It  can  also  be  reinforced  by  wire 
netting  placed  in  the  mold  before  it  is  poured.  The  specific  gravity  of 
a  sulphur-sand  mixture  (40  : 60)  was  found  to  be  2.46. 

Weight  of  1  cu.  ft 154  Ib. 

Weight  of  sulphur  required  per  cubic  feet 62  Ib. 

Weight  of  sulphur  required  per  cubic  yard 1,670  Ib. 

Taking  the  value  of  sand  as  $1  per  cu.  yd.  and  of  sulphur  as  $20  per 
ton,  the  price  of  the  materials  per  cubic  yard  will  be  about  $18.  It  may 
be  possible  to  decrease  appreciably  the  amount  of  sulphur  necessary  and 


38 


AMERICAN  SULPHURIC  ACID  PRACTICE 


hence  the  cost  by  imbedding  larger  pieces  of  crushed  rock  or  some  such 
substance  in  the  mass.  Tests  of  the  material  in  sea  water  are  being 
made,  but  it  is  too  early  to  give  results.  It  is  apparently  standing  up 
well  to  date. 

Pipes  cast  of  this  sulphur-sand  mixture  show  no  deterioration  after 
one  year  in  5  per  cent  hydrochloric  or  5  per  cent  sulphuric  acid.  The 
ordinary  organic  acids  have  no  effect  on  such  a  mixture. 

TABLE  4. — THE  PHYSICOCHEMICAL  PROPERTIES  OP  SULPHUR 


Pressure,  M  MS.  of  Mercury 

\ 

VAi 

*ORPR 
01 

essu* 

r  

WR 

F 

SULPi 

I 

/ 

/ 

q 

/ 

> 

/ 

^ 

/ 

30       2QQ       300      400 
TemfxDeg  Centigrade 

(6) 
(c) 


SP.  GR. 

2.071 
1.961 


VAPOR  PRESSURE  CURVE* 
Forms  of  sulphur: 
Crystalline 

(a)  Rhombic.     Ordinary  form  stable  below  96°C.  (205°F.) 

Monoclinic      Stable  above  96°C.  (205°F.) 

Milk  of  Sulphur.  Formed,  e.g.,  by  action  of  diluted 
acids  on  polysulphides.  Generally  called  amorphous, 
but  shown  by  Smith  and  Brownlee  to  be  crystalline.2 
There  are  several  other  modifications  of  crystalline  sul- 
phur of  scientific  interest  but  not  of  general  importance. 

Liquid.     At  113°C.  (235°F.) 1.811 

Contains : 

Sulphur  (liquid,  soluble),  Sx. 
Sulphur  (liquid,  insoluble  or  amorphous),  &n. 
The  proportion  of  Sju  to  SX  increases  with  the  temperature. 

Amorphous.     SM  (solid) 

Plastic  Sulphur.     Formed  by  heating  sulphur  above  viscous 

stage,  162°C.  or  324°F.,  and  cooling  quickly 1 . 88s 

Elastic  Sulphur.  Formed  by  heating  sulphur  above  400°C. 
or  752°F.  and  pouring  in  a  thin  stream  into  liquid  air. 
Its  elastic  properties  are  soon  lost. 

Black  Sulphur.  "  When  sulphur  mixed  with  very  little  oil  is 
thrown  into  a  hot  platinum  dish,  a  black  substance  is 
obtained  which  has  been  looked  on  as  a  modification 
of  sulphur.  The  product  contains  55  per  cent  of 
sulphur  and  33  per  cent  carbonaceous  material." — 
Watts,  Dictionary  of  Chemistry. 


1.89s 


CHARACTERISTICS  AND  USES 


39 


I  Q000450 
S.Q000400 


0000500 


0000200 


t  QOOOIOO 


150       Z&O      350     450 
Tempn  Deg  Centigrade 


The  coefficients  of  cubical  expansion  over  various  ranges  of  temperatures  are 
shown  at  horizontal  broken  lines. 


ELECTRICAL  CONDUCTIVITY1 
I 

Measured  as  reciprocal  value  of  resistivity  in  ohms  of  1  cm.  cube. 


TEMP. 


CONDUCTIVITY 


c. 

22 

69 

115 

130 
430 


F. 

72 
156 
239 
266 
806 


254 
105 
5 


0.1 


X  10-" 
X  10-" 
X  10-n 
X  10-10 
X  10-7 


Compare: 
Porcelain  

1      X  10-14 

Mica 

1      x  10-1J 

Ebonite  .  . 

1.5  X  10-» 

FRICTIONAL  ELECTRICITY 

When  rubbed  with  practically  any  other  substance,  e.g.,  glass,  fur,  silk, 
wool  or  hard  rubber — sulphur  becomes  charged  with  negative  electricity. 


COEFFICIENT  OF  LINEAR  EXPANSION1 


SURFACE  TENSION  4 


Temp. 

Temp. 

Surface  tension, 

C. 

F. 

C. 

F. 

mg./mm. 

0-13 

32-56 

0.000046 

120 

248.0 

5.71 

13-50 

56-122 

0.00007 

131 

267.8 

6.12 

50-78 

122-173 

0.00009 

146 

294.8 

6.05 

78-97 

173-207 

0.0002 

195 

383.0 

6.62 

97-110 

207-230 

0.001 

40  AMERICAN  SULPHURIC  ACID  PRACTICE 


100       200      300     400 
Temp  Deg  C 

APPROXIMATE  CURVE  OF  SURFACE  TENSION 
COMPRESSIBILITY5 

Average  fractional  change  of  volume  caused  by  1  megabar  change  in 
pressure  between  100-500  megabars  0.0000125. 

1  megabar  =  0.987  atmosphere 

CONDUCTIVITY  OF  HEAT1 

Measured  as  the  number  of  gram-calories  transmitted  in  1  sec.  through 
a  plate  1  cm.  thick  and  having  surfaces  1  sq.  cm.  in  area  when  opposite 
faces  differ  in  temperature  by  1°C. 

20°-100°C.  (68°-212°F.) 0.0006 

Compare : 

Ice 0.002 

Copper 1 . 00 

International  Atomic  Weight,  1920  =  32.06 
Vapor  Density: 

At  boiling  point  corresponds  approximately  to  formula  S813. 

At  1,000°C.  (1,832°F.)  corresponds  approximately  to  formula  S2. 

ECONOMICS  OF  NATURAL  SULPHUR 
Until  1900,  95  per  cent  of  world's  supply  from  Sicily 
In       1912,  50  per  cent  of  world's  supply  from  Sicily 
In       1917,  14  per  cent  of  world's  supply  from  Sicily 
In       1917,  80  per  cent  of  world's  supply  from  U.  S.  A. 

United  States  Exports  and  Imports 

1909  exports 37, 142  long  tons 

1909  imports 30, 589  long  tons 

1918  exports 131 ,092  long  tons 

1918  imports 82  long  tons 

United  States  Production 

1894 494  long  tons         1909 303 , 000  long  tons 

1899 1 , 590  long  tons         1914 347 , 491  long  tons 

1904 196, 888 long  tons 

1919  Texas  Gulf  Sulphur  Co. 
Only  9  months  production  after  start,  348,380  long  tons. 

PROPERTIES  OF  COMMERCIAL  SULPHUR 

Insoluble  in  Water 
Insoluble  in  Most  Acids 

Tensile  strength,  200  Ib.  per  square  inch  (approx.). 
Heat  conductivity,  low :  %  that  of  cork,  Y±  that  of  ice. 


CHARACTERISTICS  AND  USES  41 

Electrical  conductivity  lower  than  that  of  practically  any  other  solid  sub- 
stance. 
Melting  point,   depending  on  conditions,  110.2°-119.25°C.  (230.4°-246. 

rF) 

Ignition  temperature,  248°C.  (478°F.).7 
Boiling  point,  444.6°C.  (832.3°F.).« 

Melting  Point1 

—Temp.— 
Type  of  sulphur  C.  F. 

Rhombic 112.8  235 

Monoclinic 109 . 25  246  7 

Natural  freezing  point  Sx  and  S/n  in  equilibrium  (96.3  per  cent  SX,  3.7 
per  cent  SM),  110.2°C.  (230.4°F.). 

Specific  Heat1 

— Temp.— 

Type  of  sulphur  C.  F.  Sp.  ht. 

Rhombic 0-95°  32-203°  0. 1751 

Liquid 160-201  32O-393  0. 279 

201-233          393-451  0.331 

Heat  of  Combustion1 

G.  cal.  per  g.  S  B.t.u.  per  Ib. 

S  +  O2->SO2 2,200  3,960 

S ->  H2SO3  (dilute) 2,450  4,410 

S->  H2SO4  (dilute) 4,450  8,010 

Heat  of  Vaporization1 

-Temp.—  G.  Cal.  B.t.u. 

F.  per  g.  per  Ib. 

832.3°  70  126 

(Approx.) 

Transition  Temperature1 
S  Monoclinic  ±+  S  Rhombic 

Pressure,  Temp. • 

kg./sq.  cm.  Lb./in. '  C.  F. 

10.6  15  96°  204.8° 

123  175  100  212.2 

638  907  120  248 

1,350  1,920  150  302 

TRIPLE  POINT 
Sulphur 
Liquid 


Sulphur  // \\    Sulphur 

Rhombic  »  Monoclinic. 

\IZQ       1877  151*  30 


42 


AMERICAN  SULPHURIC  ACID  PRACTICE 


HEATS  OF  SOLUTION  IN  CS29 
G.  cal.  per  g. 

Dilute  solution - 11 . 89 

Saturated  solution — 11 . 55 

HEATS  OF  FusioN10 


Rhombic  at  100°C.  (212°F.) 

Monoclinic  at  100°C.  (212°F.). . . . 
To  form  pure  liquid  sulphur  (Sx) : 

From  rhombic 

From  monoclinic 


G.  cal.  per  g. 
14.9 
11.5 


B.t.u.  per  Ib. 
-21.4 
-20.9 


B.t.u.  per  Ib. 
26.8 
20.7 

26.1 
20.0 


100      ZOO     300     400 
Temp,  m  Oeg  Centigrade 

CHANGE  IN  VISCOSITY  WITH  TEMPERATURE* 
SOLUBILITIES  IN  VARIOUS  SOLVENTSU 


— Temp. — 
C.  F. 


Solubility, 

G.  i&  100-g. 

solution 

1.5 
2.1 
8.3 
46.2 
2.1 
8.0 


Amyl  alcohol 95  203 

110  230 

Aniline 89.5  193. 1 

130  266 

Benzene 25  77 

70  158 

Carbon  disulphide -20  -4  10. 5 

-10  14  13.5 

0  32  18 

20  68  29.5 

50  122  59 

100  212  92 

Carbon  tetrachloride 25  77  0.86 

Chloroform 22  71.6  1.2 

Coal-tar  oil,  sp.  gr.  0.87 15  59  2 

100  212  13 

Sp.gr.  1.02 15  59  6.5 

110  230  53.5 


CHARACTERISTICS  AND  USES 


43 


Ethyl  ether 23. 5 

Linseed  oil 15 

160 
Olive  oil  (sp.  gr.  0 . 885) 15 

130 

Sulphur  chloride 0 

55.2 
86 

Phenol 175 

Toluene 23 

Turpentine  (oil  of) 16 


74.3 

0.97 

59 

0.4 

320 

9.0 

59 

2.2 

266 

30 

32 

11 

131.4 

43 

186.8 

89 

346 

26.7 

73.4 

1.48 

60.8 

1.33 

140       160     '180 
Melting  Point  in  Deg  Centigraoe 

CHANGE  OF  MELTING  POINT  WITH  PRESSURE1 

References  Cited 

1  LANDOLT-BORNSTEIN-ROTH'S  "Physikalisch-Chemische  Tabellen"  (4th 
ed.). 

2  R.  H.  BROWNLEE,  J.  Am.  Chem.  Soc.,  vol.  29,  pp.  1032-1052  (1907). 

3  A.  WIEGAND,  Ann.  Physik,  vol.  22,  pp.  64-98  (1907). 

4  H.  ZICKENDRAHT,  Ann.  Physik,  vol.  21,  p.  141  (1906). 

5  T.  W.  RICHARDS  and  others,  Carnegie  Inst.  Pub.  No.  76,  May,  1907. 

6  MUELLER  AND  BURGESS,  J.  Am.  Chem.  Soc.,  vol.  41,  pp.  745-63  (1919). 

7  J.  R.  HILL,  Chem.  News,  vol.  95,  p.  169  (1907). 

8  Calculated   from   vapor   pressure  curve.     See   also  J.  W.  RICHARDS, 
"Metallurgical  Calculations"  (2d  ed.). 

9  M.  BELLATI  AND  L.  FINAZZI,  Atti.  r.  Inst.   Veneto,  vol.  72,  II,  pp. 
1303-14  (1913). 

10  LEWIS  AND  RANDALL,  J.  Am.  Chem.  Soc.,  vol.  33,  pp.  476-88  (1911). 

11  SEIDELL,  "Solubilities  of  Inorganic  and  Organic  Compounds"  (2d  ed.j. 

12  MOITESSIER,  Mem.  Acad.  de  Montepellier,  vol.  6,  p.  107  (1864). 

13  GMELIN-KRAUT,  "Handbuch  der  anorganishen  Chemie." 


CHAPTER  IV 
RAW  MATERIALS 

The  raw  materials  for  Sulphuric  Acid  are  sulphur,  oxygen 
(supplied  from  the  air),  and  water.  The  oxides  of  nitrogen, 
either  as  Chile  saltpeter  or  nitric  acid,  might  be  called  indirect 
raw  materials. 

Water  and  air  need  no  introduction  nor  description,  so  this 
chapter  will  be  devoted  to  the  description  of  the  sources  of 
sulphur  and  the  nitric  oxides.  The  amount  of  acid  produced  by 
distillation  from  natural  sulphates  is  practically  nothing,  leaving 
brimstone  and  the  metallic  sulphides  as  our  commercial  sources. 

Sulphur  occurk  native,  as  brimstone,  in  all  parts  of  the  world, 
particularly  rich  deposits  existing  in  Iceland  and  Sicily;  but  the 
enormous  deposits  of  Calcasiou  Parish,  south-western  Louisiana, 
furnish  the  United  States.  A  small  amount  is  mined  in  Utah  and 
Wyoming  for  local  use,  and  the  Pacific  Coast  is  supplied  from 
Japan. 

The  Louisiana  beds,  worked  by  the  Frasch  process,  were 
discovered  in  boring  for  oil,  and  a  most  interesting  and  ingenious 
method  of  recovering  the  sulphur  was  devised  by  Herman  Frasch, 
for  which  he  was  awarded  the  Perkin  medal. 

The  sulphur  ore,  containing  up  to  90  per  cent  sulphur,  occurs 
450  ft.  down,  under  quicksands  that  make  usual  mining  methods 
impossible.  The  limits  of  the  bed  have  never  been  determined, 
although  40,000,000  tons  have  been  locked  out. 

The  Frasch  process,  described  in  United  States  patents, 
No.  799,642  and  No.  800,127,  is  as  follows:  A  13-in.  hole  is  drilled 
to  a  depth  of  800  ft.,  cased,  and  inside,  concentrically,  a  10-in., 
a  3-in.,  and  a  1-in.  pipe  is  placed.  Between  the  3-in.  and  the 
10-in.,  and  the  10-in.  and  the  13-in.  pipes  superheated  water, 
heated  by  superheated  steam  to  a  temperature  where  sulphur 
begins  to  darken,  is  forced  by  its  own  expansive  force,  and  by 
steam  pressure,  into  the  deposit.  The  hot  water,  after  melting 
the  sulphur,  passes  into  the  crevices  of  the  rock,  the  molten 
sulphur  separating  from  the  water  by  gravity,  and  being  forced 
up  the  inner  pipe  by  steam  pressure.  The  steam  pressure  is 
kept  less  than  the  head  of  a  column  of  molten  sulphur  reaching 

44 


RAW  MATERIALS  45 

to  the  ground,  and  the  sulphur  is  lifted  the  last  part  of  the  way 
by  compressed  air. 

The  molten  sulphur  is  run  into  huge  spaces  fenced  in  with 
boards,  where  it  solidifies  and  is  then  blasted  down  for  shipment. 
It  will  run  over  99.6  per  cent  S,  and  practically  no  As. 

Louisiana  sulphur  is  shipped  from  Sabine  Pass,  Texas,  to 
supply  all  the  eastern  United  States.  It  was  quoted  (1916)  at 
$22  a  ton,  and  was  reported  to  cost,  f.o.b.  mines,  under  $3. 

The  Japanese  sulphur,  greyish  in  color,  comes  in  large  blocks, 
about  3  by  2  by  1  ft.,  wrapped  in  matting.  It  supplies  the 
Pacific  coast  demand. 

PYRITES 

Iron  pyrites,  FeS2,  bisulphide  of  iron,  is  one  of  the  most  widely 
distributed  of  ores,  and  has  been,  since  about  1840,  a  material 
of  prime  importance  in  the  manufacture  of  sulphuric  acid. 

Pyrites  crystallizes  in  the  regular  system,  as  a  cube,  octohedron, 
and  pyrihedron,  and  often  as  twin  crystals.  The  crystals  are 
frequently  well  developed,  and  become  very  large.  It  is  greenish 
yellow  in  color,  its  popular  name,  "Fool's  Gold,"  describing  it 
well.  Small  crystals  show  darker  colors,  and  the  powder  is 
greenish  black.  Fracture  is  conchoidal  or  irregular.  Hardness 
6  to  6.55;  sp.  gr.,  4.83  to  5.2;  it  contains  46.58  per  cent  of  iron, 
and  53.42  per  cent  of  sulphur. 

Volcanic  pyrites  contains  no  water,  while  sedimentary  deposits 
do.  Some  of  the  pyrites  containing  water  bursts  upon  roasting. 

The  principal  North  American  deposits  of  pyrites  are  at 
Tilt's  Cove;  New  Foundland;  Capleton,  Quebec;  Ely,  Vermont; 
and  Pulaski,  Virginia.  Cuba. is  becoming  .a  large  producer. 

Pyrrhotite,  magnetic  iron  sulphide,  FeySs,  is  not  a  practicable 
source  of  sulphur:  first,  because  of  its  low  sulphur  content 
(39.5  per  cent  sulphur,  60.5  per  cent  iron),  but  even  more  impor- 
tant, the  sulphur  that  it  does  contain  is  not  readily  given  up,  the 
lumps  crusting  with  oxide  of  iron,  and  extinguishing  whatever 
flame  is  started.  It  has  been  successfuly  roasted  in  powdered 
form  in  a  Herreshoff  roaster.  E.  D.  Peters  speaks,  in  "Principles 
of  Copper  Smelting"  (p.  169),  of  $200,000  thrown  away  on  an 
acid  from  pyrrhotite  proposition. 

Copper-bearing  pyrites,  of  the  general  form  of  chalcoperite, 
Cu2S,  Fe2S3,  is  a  valuable  source  of  sulphur,  either  when  the  ore 
is  roasted  and  the  S02  given  off  used  for  acid  making,  and  the 


46  AMERICAN  SULPHURIC  ACID  PRACTICE 

cinder  for  copper;  or  as  at  the  Tennessee  Copper  Co.,  the  gases 
from  semi-pyritic  smelting  are  used  direct  to  the  chambers. 

Zinc  blende,  ZnS,  the  principal  ore  of  zinc,  is  an  important  raw 
material,  the  SO2  derived  from  its  being  roasted  to  ZnO  being 
used.  Blende  contains  32.9  per  cent  sulphur  when  pure — ores 
usually  contain  some  PbS  and  other  impurities,  so  that  the 
sulphur  content  may  drop  as  low  as  20  per  cent.  Very  little 
arsenic  occurs  with  blende,  and  the  acid  produced  from  it  is  in 
demand  for  that  reason. 

The  SO2  produced  by  the  roasting  of  zinc  blende  would  prob- 
ably never  be  used  to  make  sulphuric  acid  if  the  gases  were  not 
injurious  to  vegetation,  for  the  gas  from  a  material  so  low  in 
sulphur  is  very  dilute,  ^nd  in  addition,  sufficient  air  must  be 
introduced,  not  only  to  burn  the  sulphur,  but  to  oxidize  the  zinc 
as  well: 

2ZnS  +  302  =  2ZnO  +  2S02. 

As  is  shown,  50  per  cent  more  oxygen  than  is  required  to  burn 
the  sulphur  is  required,  and  the  nitrogen  from  that  air  serves  to 
dilute  the  gas  formed.  So  sulphuric  acid  from  blende  is  less 
a  by-product  than  a  means  of  taking  care  of  the  harmful  gases, 
that  otherwise,  if  let  free,  destroy  all  vegetation  near  the  plant. 
Consequently,  while  an  important  source  of  acid  in  this  country, 
the  burning  of  blende  is  properly  a  part  of  zinc  metallurgy,  and 
for  thorough  treatment  the  reader  is  referred  to  works  on  that 
subject. 

Zinc  ores  must  be  well  roasted,  so  the  cinder  should  contain 
under  0.75  per  cent  sulphur,  either  as  ZnS  or  as  ZnSC>4.  If  the 
furnace  temperature  is  too  low  the  sulphate  will  form,  and  that 
must  be  specially  treated  to  get  it  into  the  form  of  ZnO,  for 
distillation. 

The  muffle  type  of  furnace,  with  a  mechanical  stirrer,  is  in  use 
in  all  modern  works. 

Lead  ores  are  too  low  in  sulphur  to  be  used  for  a  raw  material 
for  sulphuric  acid,  pure  galena  only  containing  13.4  per  cent 
sulphur. 

I  cannot  find  that  spent  oxide  of  iron  is  used  in  this  country  as 
a  raw  material,  although  it  is  used  abroad.  Gas  works  remove 
the  H2S  from  gas  by  a  mixture  of  hydrated  iron  oxide  and 
sawdust,  according  to  the  formula: 

Fe2(OH)  6+  3H2S  =  2FeS  +  6H20  +  S, 


RAW  MATERIALS  47 

and  upon  exposure   to  the  air  precipitates  more  sulphur,   as 
follows: 

4FeS  +  3O2  +  6H2O  =  2Fe2(OH)6  +  2S2 

This  regeneration  is  repeated  perhaps  thirty  times,  before  the 
quantity  of  sulphur  is  sufficient  to  interfere  with  the  use  of  the 
oxide  as  a  purifier.  It  contains  as  high  as  60  per  cent  sulphur 
then,  and  is  used  as  acid  material. 

NITRATE  OF  SODA 

Nitrate  of  Soda,  usually  called  Nitre,  or  Chile  saltpeter,  has 
been  the  source  of  practically  all  our  nitric  acid,  and  still  accounts 
for  the  largest  part  of  it,  although  the  various  fixation  processes 
are  making  the  nitrogen  of  the  air  available  in  ever  increasing 
quantities . 

Formula— NaNO 3 ;  hardness,  1J£  to  2;  sp.  gr.,  2.09  to  2.39; 
the  large  crystals  are  colorless,  transparent,  and  brilliant;  small 
crystals  white  and  opaque;  crystallizes  in  rhombohedra;  has  a 
bitter,  cooling  taste;  upon  heating  it  first  melts  and  then  decom- 
poses, at  a  red  heat,  into  sodium  nitrite  and  oxygen;  fuses  at 
316°C.;  and  it  dissolves  very  readily  in  water,  with  absorption  of 
heat. 

There  are  many  known  deposits  of  nitre,  but  the  world's 
supply  comes  from  northern  Chile.  There  it  is  found  under  a 
cap,  up  to  7  ft.  thick,  of  "costra,"  a  hard  conglomerate.  The 
actual  nitrate  bearing  ore,  called  "  caliche, "  occurs  in  horizontal 
beds,  up  to  5  ft.  thick,  containing  45  per  cent  to  85  per  cent 
of  sodium  nitrate,  20  per  cent  to  40  per  cent  sodium  chloride, 
and  sodium,  potassium,  and  magnesium  nitrates,  sulphates, 
iodates,  and  chlorates,  and  guano.  It  is  an  old  ocean  bed. 

The  caliche  is  crushed  and  the  soluble  salts  leached  out;  then 
the  sodium  nitrate  crystallized  out  in  a  very  pure  form,  carrying 
the  chlorates  and  iodates,  which  are  recovered  during  the  nitric 
acid  manufacture.  The  mother  liquor  retains  most  of  the  sodium 
chloride. 

An  average  analysis  of  commercial  Chile  saltpeter  is: 

96.00  per  cent  NaNO3  (including  nitrate,  iodate,  etc.), 
0.05  per  cent  NaCl, 

0.75  per  cent  sulphates  (calculated  as  Na2S04), 
2.75  per  cent  moisture. 


48  AMERICAN  SULPHURIC  ACID  PRACTICE 

The  imports  of  this  material  into  the  United  States  have  grown 
steadily,  from  125,000  tons  in  1898,  to  519,000  tons  in  1910. 
About  80  per  cent  of  this  goes  into  commercial  fertilizers,  the 
remaining  20  per  cent  into  our  chemical  industry. 

Being  deliquescent,  the  salt  becomes  damp  and  adheres  to  the 
bags  it  is  shipped  in,  not  only  causing  loss  of  nitre,  but  danger  of 
fire,  as  the  bags  will  ignite  spontaneously.  The  bags  are  therefore 
usually  washed  out  with  hot  water,  and  dried,  the  saltpeter  being 
crystallized  out  of  the  water.  The  mother  liquors  from  this 
crystallization  contain  NaNO3,  KNO3,  I,  Nal,  KI,  KC103,  20  per 
cent  to  30  per  cent  insoluble,  water,  and  small  quantities  of  borates 
and  chromates. 

The  mother  liquor  is  run  into  a  wooden  vat,  equipped  with  a 
mechanical  stirrer,  and  is  slightly  acidulated  with  sulphuric  acid; 
the  result  is  NaHS04  and  I,  from  the  iodates — now  NaN(>2  is 
added,  reacting  as  follows: 

(1)  NaN02  +  H2SO4  =  HNO2  +  NaHSO4, 

(2)  2HN02  +  2HI  =  21  +  2NO  f  2H2O, 

Bubbling  air  through  gives 

(3)  2NO  +  02  =  N204, 
which  reacts  with  HI  as 

(4)  N204  +  4HI  =  41  +  2NO  +  2H2O, 

and  the  reaction  repeats. 

Agitation  is  then  stopped,  and  the  liquor  is  allowed  to  settle 
over  night,  decanted,  filtered,  and  washed  with  soda-ash.  The 
product  is  a  paste,  running  75  per  cent  iodine  and  25  per  cent 
water. 

The  decanted  liquor  contains  0.02  per  cent  I,  which  is  treated 
with  sodium  sulphite,  to  fix  the  iodine,  so  it  will  not  pass  off  as  a 
fume,  and  goes  back  to  the  bag  house  to  be  reconcentrated.  The 
proper  amount  of  sulphite  is  known  to  have  been  added  when  the 
color  of  the  liquor  changes  from  black  to  dark  brown. 


CHAPTER  V 
PRODUCTION  OF  SO2 

By  far  the  largest  part  of  the  sulphuric  made  is  from  S02  pro- 
duced especially  for  that  purpose.  A  very  considerable  tonnage, 
however,  is  made  from  gases  which  are  b3^-products  of  certain 
metallurgical  operations. 

High  grade  brimstone  is  the  ideal  material  for  making  SO2  for 
acid  manufacture.  The  equipment  for  burning  it  is  compara- 
tively small  and  inexpensive,  and  as  it  all  burns,  there  is  no  ex- 
pense for  handling  cinder.  Moreover,  a  very  rich  and  uniform 
gas  can  be  obtained.  Several  very  satisfactory  brimstone 
burners  are  made  and  regularly  marketed  in  the  United  States. 
The  two  most  used  and  perhaps  best  suited  for  burning  large 
quantities  of  sulphur,  are  the  rotary  type  and  the  shelf  type. 

The  rotary  type  is  shown  in  Fig.  3.  This  burner  is  similar  in 
appearance  to  the  Bruckner  or  White-Howell  roasters,  except 
that  no  fire  box  is  required. 

Brimstone  melts  at  a  temperature  below  its  combustion  point, 
so  whether  it  is  in  lumps  or  in  powder  or  is  run  into  the  burner 
molten,  is  not  important  to  the  actual  burning,  although  the 
condition  in  which  it  is  to  be  fed  will  determine  the  nature  of  the 
feeding  apparatus  if  it  be  a  mechanical  one. 

If  a  pile  is  made  of  lump  sulphur  and  a  fire  started  at  the 
bottom  of  the  pile,  the  sulphur  melting  and  running  down  will 
smother  the  flame;  so  a  small  depression  is  made  in  the  top  of  the 
pile,  a  piece  of  oily  waste  lighted  and  thrown  in,  the  sulphur 
begins  to  melt  and  run  down  to  the  bottom  of  the  cavity  and  to 
take  fire.  The  pool  enlarges  itself  rapidly  by  melting  down  new 
sulphur,  and  soon  the  entire  mass  is  burning  but  all  on  the  top. 

The  molten  sulphur  is  sticky,  and  this  property  is  taken  advan- 
tage of  in  rotary  burners,  of  which  the  Glenn  Falls  Machine  Co. 
makes  the  best  known.  This  burner  is  a  plate  iron  cylinder  with 
cast  iron  truncated  cone-shaped  ends,  mounted  upon  trunnions, 
horizontally,  the  sulphur  and  air  going  in  at  one  end,  the  SO2 
and  partly  comsumed  air,  with  a  little  vaporized  sulphur,  passing 
out  at  the  other  into  a  large  fire-brick  lined  vertical  cylindrical 
4  49 


50 


AMERICAN  SULPHURIC  ACID  PRACTICE 


combustion  chamber.  In  the  combustion  chamber  entrance 
further  air  is  admitted  and  the  vapor  of  sulphur  is  completely 
burned.  (See  Fig.  3.) 

The  advantage  of  the  rotating  burner  is  that  the  molten  sulphur 
sticks  to  the  inside  of  the  cylinder  as  it  revolves  and  burns  all 
the  way  around,  which,  with  the  dripping  sulphur  adds  in  small 
compass  very  largely  to  the  combustion  area  and  so  increases  the 
capacity*  The  burner  revolves  slowly,  being  adjusted  to  have 
the  sticky  film  almost  burned  up  when  that  portion  of  the  side 
of  the  cylinder  dips  into  the  molten  sulphur  again. 


FIG.  3. 

The  labor  of  attending  these  furnaces  is  very  light.  One  man 
can  easily  feed  two  of  them  with  a  shovel  in  addition  to  looking 
after  oiling,  adjusting  dampers,  and  all  other  operation.  If  the 
sulphur  is  supplied  to  the  burners  by  mechanical  means  they 
require  very  little  attention.  The  sulphur  may  be  fed,  in  either 
the  solid  or  molten  state.  If  solid,  the  material  is  carried  into 
the  burner  from  a  small  hopper  by  a  short  screw.  If  molten,  an 
iron  tank  containing  a  steam  coil  is  placed  somewhat  above  the 
burner,  the  molten  sulphur  is  carried  to  the  burner  through  a 
steam-heated  pipe,  and  the  flow  controlled  by  a  steam-jacketed 
valve.  Either  method  works  well  if  properly  handled. 


PRODUCTION  OF  SO2  51 

Control  of  the  quality  of  gas  and  its  volume  lies  in  the  handling 
of  dampers  at  the  feed  end  and  the  entrance  to  the  combustion 
chamber,  and  in  the  quantity  of  sulphur  fed.  The  production 
of  gas  of  the  grade  most  desirable  for  making  sulphuric  acid,  i.e.t 
not  over  10  per  cent  S02  is  not  at  all  difficult.  The  chief  trouble 
which  occurs  in  the  operation  of  sulphur  burners,  especially  in 
producing  high  strength  gas,  is  that  if  dampers  are  not  properly 
adjusted  some  "sulphur  vapor  may  go  through  the  combustion 
chamber  without  being  burned.  This  sulphur  on  being  cooled 
in  the  flues  or  in  the  towers  becomes  solid  and  chokes  the 
passages. 

Rotary  burners  are  regularly  made  in  sizes  with  capacities 
ranging  from  200  to  300  lb.,  to  15  tons  per  24  hours.  Floor  space 
12  ft.  by  40  ft.  will  accommodate  even  the  largest  size  mentioned. 
The  power  consumed  in  driving  them  is  very  small. 

Rotary  type  burners  have  been  likened  to  Bruckner  roasters,  and 
the  shelf  type  may  properly  be  said  to  resemble  the  McDougall 
roaster.  It  employs  the  superimposed  tray  or  hearth  construc- 
tion. Of  course  a  stirring  mechanism  is  unnecessary  because  the 
sulphur  is  molten  and  simply  overflows  one  tray  and  drops  to  the 
next  and  so  on.  A  burner  of  this  type  is  shown  in  Fig.  4.  It  consists 
essentially  of  a  cylindrical  cast-iron  or  steel,  brick-lined  chamber 
containing  several  cast-iron  hearths  or  trays.  At  the  top  is  a 
chamber  or  reservoir  into  which  the  sulphur  is  charged  and  in 
which  it  melts.  A  valve  in  the  bottom  of  this  chamber  controls 
the  flow  of  molten  sulphur  into  the  burner  proper. 

In  operation  a  charge  of  sulphur  is  put  into  the  top  reservoir,  a 
fire  is  started  in  the  tray  immediately  below  and  allowed  to  burn 
until  the  sulphur  starts  to  melt.  The  valve  is  then  opened  and 
the  molten  sulphur  trickles  in  and  ignites.  Any  part  not  burned 
on  the  first  tray  overflows  to  the  second,  and  so  on.  Most  of  the 
ash  and  dirt  is  carried  by  the  flow  to  the  bottom  pan.  Doors 
are  provided  however  to  give  access  to  any  hearth. 

In  capacity  range  these  burners  are  regularly  made  to  burn 
up  to  10  .or  12  tons  of  sulphur  per  24  hours.  The  manufacturers 
point  out  the  following  advantages  for  this  type  of  burner: 

1.  No  moving  parts  or  power  required. 

2.  Small  floor  space.     A  9-ft.  diameter  cylinder  burns  10  to  12 
tons  per  24  hours. 

3.  Better  heat  conservation  than  any  other  type. 

As  mentioned  before,  brimstone  burning  allows  the  production 


52 


AMERICAN  SULPHURIC  ACID  PRACTICE 


of  very  rich  and  uniform  gas.     The  percentage  of  S02  is  limited 
by  the  fact  that  for  either  chamber  or  contact  work  a  certain 

minimum  oxygen  percentage  must  be  maintained.     This  oxygen 

SO 
percentage  should  be  at  least  per  cent  —~  +  4,  since  one  volume 


FIG.  4. 


of  SO 2  requires  y%  of  one  volume  of  oxygen  to  form  S03,  and  about 
4  per  cent  excess  is  desirable.  Since  air  contains  about  20.8  per 
cent  oxygen,  the  sum  of  SO2  and  oxygen  in  the  gas  from  the 
burner  will  be  20.8  per  cent.  The  maximum  S02  then  should 


PRODUCTION  OF  S02  53 

be,  in  accordance  with  the  above  proportion,  11.2  per  cent  and 
oxygen  9.6  per  cent. 

BURNING  PYRITES 

Iron  pyrites,  when  pure,  has  the  formula  FeS2,  and  contains 
46.7  per  cent  iron  and  53.3  per  cent  sulphur.  It  is  never  obtained 
entirely  pure,  although  material  containing  over  50  per  cent  sul- 
phur is  sometimes  found.  The  general  range  is  from  40  per  cent 
to  50  per  cent  sulphur. 

Sulphides  of  the  metals  burn  in  air,  with  the  production  of  the 
metallic  oxides  and  SO2;  and  if  the  operation,  called  roasting,  is 
not  complete,  intermediate  sulphates  and  bisulphates. 

Iron  pyrites  when  roasted  gives  off  of  its  FeS2  nearly  one  atom 
of  sulphur  very  easily.  At  comparatively  low  temperatures  the 
sulphur  burns  at  once  to  S02  leaving  behind  Fe7Ss.  At  higher 
temperatures  it  is  at  first  volatilized  as  a  dense  cloud  of  yellow 
smoke,  and  then  burns  to  SO2.  At  the  second  stage  of  the  process 
begins  the  oxidation  of  the  iron  in  the  ore  along  with  that  of  the 
remaining  sulphur.  This  is  much  slower  and  less  vigorous  than 
the  burning  of  the  primary  atom  of  sulphur,  and  as  the  various 
iron  oxides  formed  are  fairly  active  catalytic  agents  or  "  contact 
substances,"  a  considerable  quantity  of  SO3  is  formed  at  this 
stage.  For  purposes  of  calculation  the  net  result  of  these 
reactions  may  be  written: 

4FeS2  +  1102  =  2Fe2O3  +  8S02 

Pyrites  is  obtained  and  burned  in  two  different  forms,  viz., 
as  lump  pyrites  and  as  fines.  The  former  is  material  in  pieces 
from  the  size  of  the  fist  down  to  about  %  in.  Fines  is  material 
under  J£  in.  These  two  classes  are  burned  in  distinctly  different 
forms  of  burners. 

The  lump  burners  used  in  this  country  are  quite  simple.  The 
general  scheme  is  similar  to  the  burning  of  lump  coal  on  grates 
except  that  the  bed  of  fire  is  carried  much  deeper,  i.e.,  around  2 
ft.  Fines  in  any  appreciable  amount  are  not  permissible  as  they 
prevent  free  draught.  In  brief,  a  single  burner  consists  of  a 
brick  box  up  to  6  ft.  long  from  front  to  back,  and  4  or  5  ft.  wide. 
It  is  divided  by  a  grate  into  an  upper  or  burner  compartment, 
and  a  lower  or  ash  pit  compartment.  A  charging  door  is  placed 
at  such  a  level  above  the  grate  as  to  allow  a  bed  of  ore  about  2 
ft.  deep.  A  small  door  at  the  grate  level  allows  the  grates  to  be 


54 


AMERICAN  SULPHURIC  ACID  PRACTICE 


shaken.  A  door  in  the  ash  pit  provides  for  removal  of  cinder. 
Grate  bars  made  of  cast  iron,  of  square  section  about  2  in.  on  a 
side  are  used.  They  are  supported  by  cast-iron  bearers  at  two 
or  three  points.  The  bars  are  made  with  circular  section  at  the 
points  of  support  in  order  that  they  may  be  turned.  When 
their  diagonals  are  set  vertical  and  horizontal  a  considerably 
smaller  space  exists  between  them  than  when  they  are  turned 
with  their  diagonals  45°  from  horizontal.  By  turning  the  bars 
from  one  position  to  the  other  with  a  wrench  the  lumps  are 
crushed  and  the  shaking  out  of  the  spent  cinder  is  accomplished. 
Figure  5  shows  the  general  features  of  a  lump  burner  and  grates. 
Most  of  the  modern  plants  using  the  lump  burner  have  im- 
proved its  details  making  it  tighter  and  more  convenient  to 
operate.  Burners  are  now  made  practically  encased  in  steel  or 


Circular  Sect     C.T.Grate to*r± 


Normg)  '  Position 


Q  D  Q  Turned  for. 

Removing  Cinder 


FIG.  5. 


cast-iron  plates.  Door  frames  and  doors  are  planed  to  give 
tight  joints  without  using  putty.  In  some  cases  the  ash  pits 
discharge  into  cars  in  a  tunnel  below  the  burner  set.  These 
improvements  have  made  labor  less  and  gas  more  uniform,  but 
the  nature  of  this  form  of  burner  demands  a  considerable  amount 
of  hand  labor  which  cannot  well  be  eliminated. 

The  capacity  of  a  burner  depends  somewhat  upon  the  sulphur 
tenor  of  the  ore  and  its  melting  point.  High  grade  pyrites  con- 
taining little  copper  can  be  burned  to  give  much  more  S02  per 
unit  of  grate  area  than  low  grade  ore  high  in  copper  or  which 
contains  pyrrhotite;  in  other  words  ore  of  low  fusing  point.  We 
cannot  in  any  event  expect  to  get  much  more  than  one  ton  of 
60°  acid  from  one  good  sized  burner.  Driving  a  burner  too  fast 
causes  fusing  and  sticking  and  much  hot  laborious  effort  to  clean. 

It  will  be  seen  that  to  provide  gas  for  a  large  set  of  chambers 
the  ground  area  and  buildings  required  for  lump  burners  is  very 
great.  Lump  burners  are  built  in  blocks  back  to  back  and 
consisting  of  almost  any  number  desired.  Sets  of  24  to  30  are 


PRODUCTION  OF  S02  55 

common,  and  some  up  to  40  are  to  be  seen.  To  decrease  ground 
area  the  obvious  thing  to  do  would  be  to  carry  greater  depth  of 
ore  on  the  grates.  This  presents  several  difficulties  however. 
Heat  would  get  too  high  if  rate  of  burning  per  square  foot  were 
increased.  Shaking  out  cinder  uniformly  would  be  uncertain. 
If  fusing  occurred,  cleaning  would  be  difficult.  Burning  of 
lump  pyrites  is  practiced  almost  entirely  on  acid  units  of  not 
over  50  tons  60°Be.  acid  daily  capacity. 

INSTRUCTIONS  FOR  STARTING  LUMP  BURNERS 

Be  sure  the  brickwork  is  not  too  green  upon  starting.  The 
moisture  should  be  dried  out  of  the  bricks  by  means  of  a  very 
light  fire  in  the  bottom  before  starting  up. 

Uniformity  of  size  of  charge  is  important  and  money  spent  on 
this  will  pay  well. 

First  clean  out  the  furnaces  thoroughly;  see  that  the  top  flues 
are  clean;  put  in  the  grate  bars.  See  that  all  doors  are  in  place. 
Manhole  doors  should  have  a  thin  joint  of  tar  and  fireclay. 

The  top  buckstay  rods  should  not  be  too  tight,  which  is  readily 
seen  by  striking  them  with  a  hammer,  so  as  to  allow  for  expan- 
sion as  the  furnace  heats  up.  This  must  be  watched  carefully. 

Before  putting  a  fire  in  the  furnace  provision  should  be  made 
for  taking  off  the  smoke,  which  is  best  done  by  means  of  a  tempo- 
rary stack  on  the  uptake  to  the  Glover  tower,  over  the  opening 
in  one  of  the  top  plates.  This  stack  should  have  a  tight  damper 
in  it  so  it  will  not  be  necessary  to  remove  it  when  its  use  is  dis- 
continued. 

The  damper  in  the  Glover  flue  must  be  closed  to  prevent  smoke 
from  getting  into  the  system.  It  is  necessary  to  cover  the  grate 
bars  with  something  like  pyrites  cinder  to  protect  them  from 
warping.  If  cinder  is  not  to  be  had,  broken  stone  or  brick  will 
do.  Spread  out  this  protector  a  foot  thick  except  in  the  corners, 
where  it  should  be  15  in.  A  wood  fire  is  then  started  in  each 
furnace  on  top  of  the  cinder.  The  fire  is  kept  burning  until  the 
whole  interior  is  well  warmed  up  and  there  is  a  bed  of  red  ashes 
over  the  entire  area  of  the  furnaces.  The  fire  is  then  increased 
until  the  interior  of  the  furnaces  is  red  hot,  including  the  top  of 
the  bed  of  cinders. 

The  best  material  for  firing  is  oak  or  hickory  as  these  make  little 
smoke.  Broken  coke  and  coal  are  used  but  as  these  make  a  very 


56  AMERICAN  SULPHURIC  ACID  PRACTICE 

hot  fire,  care  must  be  taken  that  no  clinkers  are  formed  with 
the  cinder.  If  any  are  formed  they  must  be  removed  before 
changing  ore. 

As  the  mass  of  brickwork  and  iron  is  bound  to  expand  as  it 
heats  up,  the  buckstay  rods  must  be  loosened  from  time  to  time. 
A  tap  with  a  hammer  shows  if  they  are  too  tight,  a  hard  metallic 
ring  indicating  that  they  should  be  slacked  off.  Do  not  loosen 
them  too  much  as  it  is  hard  to  tighten  them  again  owing  to  the 
great  pressure  of  the  arches,  which  may  crack  in  consequence. 
Care  must  be  taken  that  a  furnace  does  not  get  hot  too  quickly. 
Firing  should  take  30  to  36  hours  for  a  new  furnace,  less  time 
being  required  for  an  old  one  being  restarted. 

After  the  final  heating  the  wood  should  be  burned  off  about  the 
same  time  in  each  furnace,  leaving  a  bed  of  hot  embers.  Before 
ore  is  charged  withdraw  any  unburned  fuel,  at  the  time  making 
sure  there  is  no  matte  where  the  main  fire  was.  Distribute  the 
hot  embers  evenly  then  charge  sufficient  pyrites  to  cover  the 
whole  grate.  The  pyrites  should  be  placed  in  front  of  the  fur- 
naces beforehand  so  that  no  time  is  lost  in  charging,  for  it  is 
very  important  that  they  go  in  quickly  before  the  furnaces  lose 
heat.  This  is  best  done  by  having  several  men  charging  at  the 
same  time.  When  the  charges  are  in,  the  gas  can  be  turned 
into  the  system.  When  the  first  charge  is  burning  well,  the 
furnaces  should  receive  a  second  charge  so  as  to  insure  a  suffi- 
cient quantity  of  ore  in  the  furnace  to  prevent  any  possibility 
of  running  low  and  losing  its  heat. 

The  gases  leaving  the  furnace  contain  for  a  time  some  carbon 
dioxide  in  addition  to  S02,  due  to  the  residual  fuel.  It  is  highly 
important  to  charge  the  furnaces  with  clock-like  regularity.  For 
example,  if  there  are  24  furnaces  one  will  be  charged  every  hour  or 
every  half  hour  as  desired.  A  regular  schedule  is  followed  in 
any  event.  The  charging  time  of  each  furnace  should  be  marked 
upon  it. 

FINES  BURNERS 

Fines  burners  are  by  far  the  most  used  and  most  important 
of  the  apparatus  for  producing  SO2  for  making  sulphuric  acid. 
The  main  reasons  for  this  are : 

1.  Large  capacity  with  small  ground  area. 

2.  Charging  ore  and  discharging  cinder  are  continuous  and  are  accom- 
plished without  opening  the  furnace,  and  the  gas  is  in  consequence  uniform. 


PRODUCTION  OF  S02  57 

3.  Handling  of  ore  and  cinder  are  done  by  machinery,  practically  elimi- 
nating hand  labor. 

4.  Several  well-designed  and  satisfactory  furnaces  are  on  the  market  and 
can  be  bought  practically  from  stock. 

In  the  early  days  of  acid  making  pyrites  fines  were  burned  in 
the  crudest  way.  The  favorite  method  was  on  a  brick  hearth, 
the  pyrites  being  fed  by  hand  with  shovels,  and  rabbled  by  hand. 
This  method  produced  cinder  high  in  sulphur  and  most  ununi- 
form,  besides  being  very  costly  in  labor. 

The  first  improvements  over  the  hand  method  in  rabbling 
were  along  the  line  of  mechanical  rabbles  in  the  form  of  plows 
which  were  dragged  through  the  furnace  on  a  chain,  pulling 
the  ore  along  with  it  and  turning  it  over,  giving  a  much  better 
roast  with  lower  labor  costs.  But  to  get  a  complete  roast  the 
temperature  had  to  be  high  and  maintenance  costs  were  heavy. 
Also  the  plows  were  heavy  and  the  wear  on  the  hearths  consider- 
able. 

The  next  step  was  an  annular  furnace  with  arms  branching 
out  from  a, revolving  central  axis,  the  arms  carrying  rakes  for 
stirring  the  ore.  The  roof  of  the  furnace  had  to  be  supported 
from  the  outside  as  the  arms  entered  the  furnace  through  a 
slot  in  the  inner  wall.  A  great  deal  of  air  entered  through  this 
slot  so  it  was  often  covered  by  an  iron  apron  revolving  with 
the  arms. 

In  1868,  McDougall  introduced  his  circular  multiple  hearth 
furnace.  The  McDougall  furnace  consists  essentially  of  a 
cylindrical  steel  shell  lined  with  about  9  in.  of  brick  and 
containing  several  self -supporting  arched  brick  hearths.  Through 
the  center  of  the  furnace  runs  a  vertical  iron  shaft  or  column. 
To  it  are  fastened  horizontal  iron  arms,  one,  two,  or  even  three 
to  each  hearth,  and  these  bear  iron  rabble  teeth.  This  shaft 
with  its  arms  is  supported  on  a  bearing  beneath  the  furnace 
and  in  operation  is  revolved  slowly.  Alternate  hearths  have 
drop-holes  near  the  central  column  and  near  the  outside  wall. 
The  rabble  teeth  stir  the  burning  ore  and  move  it  across  the 
hearths  so  that  it  passes  uniformly  down  through  the  furnace, 
crossing  each  hearth  and  falling  to  the  one  below. 

The  original  McDougall  furnaces  did  not  include  any  provision 
for  keeping  the  shaft  and  arms  and  rabbles  cool,  and  this  was 
probably  the  chief  reason  that  the  furnace  gave  trouble  and  was 
not  more  widely  used  for  many  years.  Mr.  J.  B.  F.  Herreshoff 


\ 
58  AMERICAN  SULPHURIC  ACID  PRACTICE 

of  the  Nichols  Chemical  Co.  on  investigating  the  problem  built 
a  furnace  with  a  hollow  iron  shaft  and  hollow  arms,  and  blew 
cold  air  through  them,  in  that  way  keeping  the  temperature  of 
the  metal  at  such  a  point  that  its  strength  was  not  impaired. 
Herreshoff  also  arranged  to  admit  controlled  amounts  of  the  heated 
air  issuing  from  the  shaft  and  arms,  into  the  hearths  at  any 
desirable  points.  Frasch  also  applied  water  cooling  to  the  hollow 
shaft  and  arms. 

Other  improvements  and  refinements  have  been  made  on  the 
McDougall  furnace  and  we  find  to-day  that  the  name  McDougall 
has  largely  disappeared,  and  these  furnaces  are  known  by  the 
names  of  those  who  have  made  the  modifications. 

The  chief  differences  in  the  furnaces  of  this  type  now  on  the 
market  are  in  the  shafts  and  arms,  and  the  following  classification 
is  made  on  that  basis: 

1.  Furnaces  having  water-cooled  shafts  and  arms. 

2.  Furnaces  having  air-cooled  shafts  and  arms. 

3.  Small  shaft  furnaces,  i.e.,  shafts  into  which  a  man  cannot  enter. 

4.  Large  shaft  furnaces,  i.e.,  shafts  large  enough  to  allow  a  man  to  enter 
and  work. 

In  roasting  any  of  the  pyritic  materials  suitable  for  acid  making 
it  should  be  understood  that  furnace  temperatures,  i.e.,  tempera- 
tures of  gas,  ore,  and  brickwork,  are  influenced  only  to  a  small 
extent  by  either  the  air  or  water  which  may  be  circulated  through 
the  shaft  and  arms.  This  statement  applies  in  greater  degree 
to  large  than  to  small  furnaces.  The  prime  function  of  the  air  or 
the  water  is  to  regulate  the  temperature  of  the  iron  parts  them- 
selves. A  rough  heat  balance  sheet  of  a  roaster  burning  a  pyritic 
ore  of  moderate  sulphur  tenor  is  interesting  in  showing  the  dis- 
posal of  the  heat  units. 

As  this  balance  is  intended  to  show  only  the  relative  amounts 
of  heat  going  to  the  various  products,  etc.,  rather  than  acutal 
heat  units,  only  the  iron  sulphid  is  considered. 

This  ore  contains  34.7  per  cent  S  as  FeS2. 

The  calcine  contains  7.0  per  cent  S. 

The  calcine  weight  is  80  per  cent  of  that  of  the  ore  from  which  it  is  made. 

For  each  100  parts  of  ore  there  is  burned  34.7-80  per  cent  of  7  or  29.1 
parts  of  sulphur 

Assume  that  one  half  this  is  "volatile  atom"  and  its  dissociation  heat 
requirement  is  negligible.  The  heat  evolvers  are  then: 


PRODUCTION  OF  SO2  59 

29.1  parts  S  to  SO2  @  2,170  calories  =  63,200 

29.7  X  1.75  parts  Fe  to  Fe2O3  @  1,750  calories  =  44,500 
Total  calories  per  100  parts  ore  =  107,700 

Heat  is  absorbed  by  dissociation  of  FeS. 

40  FeS  @  273  calories  =  10,920 

Net  calories  evolved  per  100  parts  ore  =  •  96,780 

Assume  that  the  furnace  roasts  100  Ib.  ore  per  minute  and  that 
the  gas  issuing  from  it  contains  9  per  cent  SO2,  8  per  cent 
oxygen  and  83  per  cent  nitrogen. 

29.1  Ib.  S  make  320.6  cu.  ft.  SO2.  Total  gas  per  minute  then  = 
3,562  cu.  ft.  Assume  the  air  enters  the  furnace  at  20°C.  and  the 
gas  leaves  it  at  620°C.  Then  the  heat  carried  away  by  the  gas  is : 

SO2 09  X  3,562  (.0226  X  600  X  .0000187;  =  10.80 

0 08  X  3,562  (.0189  X  600  X  .0000017)  =    5.65 

N 83  X  3,562  (.0189  X  600  X  .0000017)  =  59.80 

Calories  per  degree < . .  75 . 35 

Calories  for  600°  =  45,210. 
Calcine  from  100  Ib.  ore  =  80  Ib. 

The  ore  enters  the  furnace  at  20°C.  and  the  calcine  is  discharged 
at  420°C.  Heat  carried  away  by  calcine  is  80  (.1456  X  400  X 
.000188)  =  17.664  pound  calories  per  degree.  Calories  for 
400°  =  7,066. 

This  furnace  is  assumed  to  be  air  cooled.  There  are  1,000 
cu.  ft.  per  minure  of  air  at  20°C.  blown  in  through  the  arms,  and 
this  air  issued  at  220°C.  Calories  carried  away  by  this  air  = 

3,848. 

RECAPITULATION 
Total  heat  envolved  =  96,780  calories 

Heat  to  gas 45,210 

Heat  to  calcine 7,066 

Heat  to  air 3,848 

Total  accounted  for 56, 124 

Balance  for  radiation 40,650 

Radiation  surface  of  the  furnace,  2,200  sq.  ft. 
Loss  per  square  foot  per  minute  =  18.4  Ib.  calories. 

This  calculation  shows  that  the  two  chief  ways  in  which  the 
heat  is  carried  off  from  a  roasting  furnace  are  by  the  gas  and  by 
radiation.  The  heat  units  carried  away  by  the  cooling  medium 
circulated  through  the  shaft  and  arms,  and  by  the  calcine,  are 


60  AMERICAN  SULPHURIC  ACID  PRACTICE 

insignificant.  As  the  radiating  capacity  of  a  furnace  once  built 
is  not  variable  at  will,  it  is  apparent  that  control  of  furnace 
temperature  must  lie  in  feed  of  ore  and  volume  of  air  admitted. 
When  air  cooling  of  the  iron  parts  can  properly  be  used  it  is  to 
be  preferred  over  water  cooling  for  several  reasons.  When  water 
is  used  for  cooling,  the  temperature  of  the  arms  is  so  low  that  the 
iron  becomes  sulphated  and  the  rabbles  soon  become  cemented  to 
the  arms  and  can  often  be  removed  only  by  breaking.  With 
air  cooling,  the  temperature  of  the  metal  is  usually  so  high  that 
this  sulphating  does  not  occur.  Another  advantage  is  that  slight 
leaks  at  joints  or  chaplet  plugs  do  no  harm  if  air  cooling  is  em- 
ployed, while  with  water  even  slight  leaks  cannot  be  tolerated. 
Often  a  water-cooled  arm  must  be  removed  on  account  of  a 
persistent  small  water  leak  where  an  air  leak  of  the  same  size 
would  scarcely  be  noticed. 


RibforRabbte 


Air-Cooled  Arm    Flanged  End 


Water-Cooled  Arm  Wedge  Type  Arm  End 
FIG.  6. 


Q 


Air-cooled  arms  and  shaft  must  have  much  larger  passages  in 
them  than  necessary  when  water  is  used  for  cooling.  Indeed  the 
success  or  failure  of  air  cooling  depends  much  upon  whether  or 
not  the  passages  are  of  ample  area.  The  thickness  of  metal  in 
air-cooled  arms  is  less  than  in  water-cooled  arms. 

Figure  6  shows  the  essential  features  of  an  air-cooled  arm  with 
flanged  end  for  bolting  to  shaft,  and  a  water-cooled  arm  with 
end-detail  as  used  in  the  Wedge  furnace. 

The  other  major  difference  in  the  McDougall  types  is  in  the 
large  and  small  central  columns.  Until  the  advent  of  the  Wedge 
furnace  all  the  McDougall  furnaces  had  small  central  columns, 
i.e.,  not  above  18  or  20  in.  diameter,  and  hence  too  small  for  a  man 
to  enter.  When  anything  became  wrong  with  an  arm  which 
necessitated  replacing  it,  it  was  necessary  to  stop  the  furnace  and 


PRODUCTION  OF  SO2  61 

allow  it  to  cool  down  enough  to  permit  men  to  enter  the  hearth, 
unfasten  the  bad  arm  from  the  shaft  and  fasten  on  a  new  one. 
This  always  required  several  days  and  meant  that  the  furnace 
had  to  be  restarted  with  fuel.  Such  a  loss  of  time  is  a  serious 
thing  to  an  acid  plant,  especially  if  a  single  furnace  is  being 
depended  upon. 

Many  attempts  have  been  made  to  devise  arrangements 
whereby  arms  could  be  replaced  without  cooling  and  entering  the 
hoarths.  It  is  not  difficult  to  do  this  if  air  cooling  or  no  cooling 
is  sufficient.  If  water  cooling  is  necessary  and  water-tight  con- 
nections have  to  be  made  it  seems  impossible  unless  one  can  get 
at  the  inner  end  of  the  arm,  which  with  the  small  column  furnace 
means  getting  into  the  hearth.  While  this  feature  of  the  small 
shaft  furnaces  is  disagreeable,  it  should  not  be  overestimated. 
Well  made  arms  properly  taken  care  of  last  for  long  periods,  and 
there  are  other  things  beside  failure  of  arms  which  demand 
cooling  down  a  furnace  at  times,  failure  of  brickwork  for  example. 
It  is  often  possible  to  get  along  with  a  sick  arm  for  a  time  until  a 
general  overhauling  is  desirable. 

Small  column  furnaces  of  which  the  Herreshoff  is  an  example 
have  their  columns  made  up  of  cast-iron  sections  flanged  together. 
When  water  cooling  is  used  a  water  supply  pipe  extends  down 
the  middle.  It  is  provided  with  a  tee  fitting  corresponding  to 
each  arm,  into  which  is  screwed  a  pipe  which  extends  well  out 
toward  the  end  of  the  arm.  The  water  enters  the  arm  through 
this  pipe  and  returns  around  it  into  the  annular  space  in  the 
column.  Usually  the  arm  itself  has  a  flanged  end  which  is 
bolted  to  a  corresponding  flange  on  the  column  casting.  There 
are  variations  in  this  method  of  fastening  but  the  flange  is  most 
used. 

For  air  cooling  a  partitioned  arm,  as  shown  in  Fig.  6,  is  used 
and  an  interior  column  construction  as  shown  in  Fig.  5. 

The  Wedge  furnace,  shown  in  Fig.  65,  is  the  only  furnace  made 
with  the  large  column.  This  column  is  4  or  5  ft.  in  internal 
diameter,  built  of  steel  plates  riveted  together,  and  covered  on 
the  fire  side  with  fire  brick  and  insulating  material.  The  arms 
project  through  the  wall  of  this  column  and  are  fastened  inside. 
The  air  or  water  connections  are  likewise  inside  the  column. 
It  is  a  simple  matter  in  case  of  the  failure  of  an  arm  for  a  man  to 
enter  the  column  immediately,  disconnect  the  pipes,  and  loosen 
the  latch.  The  arm  can  then  be  pulled  out  and  a  new  one  in- 


62 


AMERICAN  SULPHURIC  ACID  PRACTICE 


FIG.  6 A. — Herreshoff  furnaces. 


PRODUCTION  OF  SO, 


63 


serted  and  connected.  It  is  not  a  pleasant  job  because  the  inside 
of  the  column  is  decidedly  warm,  but  it  can  be  readily  and  safely 
done  by  any  men  who  are  reasonably  accustomed  to  furnace 
work.  There  are  certainly  many  more  severe  tasks  about  metal- 
lurgical furnaces.  If  proper  arrangements  are  made  an  arm 
may  be  removed  and  a  new  one  inserted  and  connected  ready  to 
go  in  4  hours. 


FIG.  GB. 

One  feature  of  the  large  column  which  has  given  some  trouble 
is  the  carrying  of  the  great  rotating  weight  in  a  satisfactory  way. 
The  customary  design  for  the  larger  sizes  provides  a  set  of  six 
large  beveled  rollers  upon  which  the  cast  spider  carrying  the 
column  revolves.  In  the  middle  is  a  small  guide  bearing.  The 
trouble  with  this  arrangement  is  in  maintaining  the  shaft  plumb, 
and  the  load  equally  distributed  upon  the  rollers.  The  side 


64  AMERICAN  SULPHURIC  ACID  PRACTICE 

thrust  causes  some  wear  of  the  rollers  and  their  thrust  bearings, 
which  is  not  equal  all  the  way  around.  As  soon  as  one  roller  is 
further  away  from  the  center  than  the  others  it  ceases  to  carry  its 
proper  share  of  the  load,  or  else  the  shaft  goes  out  of  plumb. 
This  cannot  be  said  to  be  a  very  serious  fault,  but  it  makes  the 
arrangement  less  satisfactory  than  the  old  step  bearing. 

In  the  25-ft.  furnaces  of  this  type  erected  at  Anaconda  a  few 
years  ago,  the  columns  are  supported  on  9-in.  step  bearings  of 
very  rugged  construction.  The  column  is  held  plumb  by  a  set 
of  vertical  rollers  bearing  against  a  ring  fastened  around  the  top 
of  the  column. 

Fines  burners  are  started  by  bedding  the  upper  floors  with  ore 
then  heating  with  wood,  coal,  oil,  gas,  or  powdered  coal,  with  the 
mechanism  stationery.  When  sufficiently  heated  the  floors  are 
cleared  and  the  mechanism  started  with  a  light  feed  of  ore.  It 
is  usually  necessary  to  use  a  little  fuel  for  a  time  after  starting 
feed.  The  variables  used  in  the  control  of  a  furnace  are  amount 
of  ore  fed,  and  volume  of  air  admitted,  also  sometimes  the  rate 
of  revolution  of  the  arms.  The  usual  speed  of  revolution  is  from 
1  to  2  R.P.M.  The  operation  is  watched  through  peep-holes. 
A  15-ft.  (diameter)  furnace  requires  one  horse  power. 

BY-PRODUCT  GAS  FROM  COPPER  REDUCTION  WORKS 

About  one-half  million  tons  per  year  of  acid  is  made  from  gases 
evolved  from  the  reduction  of  copper  ore.  The  only  two  sources 
of  such  gases  at  present  are  roasting  furnaces  and  blast  furnaces. 
The  roasting  furnaces  used  at  copper  reduction  works  in  con- 
nection with  acid  making  are  all  of  theMcDougall  type,  and  of 
several  different  makes,  embracing  all  the  types  described  above. 
The  materials  roasted  show  wide  range  and  are  all  materially 
different  from  the  pyrites  ores  regularly  bought  for  acid  making. 
However  as  the  gas  used  is  really  a  waste  product  and  no  charge 
for  sulphur  is  made  against  the  acid,  these  acid  plants  can  well 
afford  to  work  with  less  favorable  ores. 

The  chief  difference  between  the  materials  available  at  copper 
reduction  works  and  the  ordinary  ores  is  that  the  former  are 
lower  in  sulphur  and  higher  in  copper,  are  of  irregular  analysis, 
and  are  often  exceedingly  fine.  While  pyrites  ores  range  from 
40  per  cent  to  50  per  cent  sulphur  and  contain  little  copper,  the 
ores  and  concentrates  used  at  copper  works  range  from  25  per 


PRODUCTION  OF  SO2  65 

cent  to  40  per  cent  sulphur,  and  contain  up  to  12  per  cent  or  15 
per  cent  copper.  Moreover  at  some  plants  the  sulphur  content 
of  the  material  varies  5  to  10  per  cent  from  day  to  day. 

The  copper-iron  sulfide,  and  the  copper  sulfide  minerals  fuse 
at  a  considerably  lower  temperature  than  does  straight  pyrites, 
so  in  roasting  copper  ores  and  concentrates  accretions  are  found 
to  form  on  the  brickwork  and  on  the  shaft  of  the  furnace  much 
more  than  they  do  when  roasting  pyrites.  This  fact  makes  it 
necessary  to  watch  the  furnace  temperatures  carefully  or  serious 
formations  of  matte  may  occur.  A  good  deal  of  barring  and 
plowing  of  the  hearths  is  necessary  even  with  the  most  careful 
attention. 

As  the  cinder  from  the  roasted  copper  ore  is  usually  treated  in 
a  reverberatory  furnace  to  make  a  copper  matte,  some  sulphur 
should  be  left  in  the  cinder.  For  example  at  Anaconda  where 
the  copper  content  of  the  cinder  is  about  10  per  cent,  it  is  desirable 
to  leave  about  7  per  cent  sulphur  in  the  cinder  to  make  matte. 

THE  BLAST  FURNACE 

The  blast  furnace  is  a  very  unusual  source  of  S02  for  acid  mak- 
ing. The  only  place  in  this  country  where  it  has  been  used  is 
at  the  reduction  works  of  the  Tennessee  Copper  Co.  and  the 
Ducktown  Sulphur,  Copper,  and  Iron  Co.,  in  the  Ducktown 
district  in  southeastern  Tennessee.  There  exists  a  peculiar  set 
of  conditions  there  which  will  rarely  be  duplicated,  but  the  ton- 
nage of  acid  produced  is  so  large,  and  the  plants  themselves 
present  so  much  of  interest  in  their  construction  and  operation, 
that  some  description  of  the  operations  is  in  order. 

The  ore  treated  at  these  works  is  a  heavy  sulfide  carrying 
substantially : 

PER  CENT 

Copper 2.5 

Iron 30.0 

Sulphur 20. 0 

Insoluble.  . 30. 0      . 

CaO,  MgO 10.0 

Zinc 3.0 

A12O3 3.0 

This  ore  is  treated  directly  in  blast  furnaces  with  no  prelimi- 
nary dressing  or  concentration  whatever.  It  is  very  near  self- 
fluxing  when  making  a  1 5  per  cent  copper  matte,  and  it  can  be 
smelted  with  about  5  per  cent  coke.  This  permits  the  production 


66  AMERICAN  SULPHURIC  ACID  PRACTICE 

of  a  gas  containing  7  per  cent  to  8  per  cent  SO2,  5  per  cent  to  6  per 
cent  CO 2,  and  about  3  per  cent  to  4  per  cent  oxygen. 

At  the  time  the  first  acid  plants  were  built,  about  1907,  no 
experience  was  available  to  say  what  could  be  done  with  such 
gas.  However  it  was  necessary  to  undertake  the  manufacture 
of  acid  because  the  United  States  Supreme  Court  had  enjoined 
the  smelteries  from  allowing  to  escape  more  S(>2  than  the  state 
of  Georgia  deemed  reasonable.  The  redeeming  feature  of  the 
situation  lay  in  the  fact  that  Ducktown  basin  is  in  the  heart  of 
that  portion  of  the  country  which  consumes  the  greater  part  of 
all  the  acid  phosphate  fertilizer  made  in  the  United  States,  that 
is  to  say  there  is  an  excellent  market  for  sulphuric  acid. 

For  some  time  after  the  completion  of  the  plants  troubles  of 
various  kinds  were  experienced  and  many  curious  phenomena 
arose.  The  chief  differences  between  this  blast  furnace  gas 
and  the  gases  usually  used  for  making  sulphuric  acid  are  the 
high  C(>2  content  and  the  low  oxygen.  It  was  necessary  to 
revise  ideas  about  the  oxygen  content  of  exit  gases,  or  else  if 
the  customary  6  per  cent  were  maintained  there,  to  take  a  gas 
entering  at  about  2  per  cent  to  3  per  cent  SC>2.  One  solution  of 
this  devised  at  the  Ducktown  plant,  was  to  adjust  the  gas  enter- 
ing to  contain  about  3  per  cent  oxygen,  and  to  introduce  air  into 
each  chamber  sufficient  to  maintain  3  to  4  per  cent  oxygen  at  all 
stages  of  the  process.  Working  without  this  arrangement  the 
best  way  seemed  to  keep  the  oxygen  in  the  exit  gases  above  2  per 
cent  and  get  as  good  S02  entering  as  that  would  allow. 

It  should  perhaps  be  explained  that  in  near-pyritic  smelting 
the  gases  issuing  from  the  charge  contain  almost  no  oxygen  and 
if  the  furnace  top  and  flues  are  tight  the  gas  entering  the  acid 
plant  contains  only  such  oxygen  as  may  be  voluntarily  admitted. 

The  high  percentage  of  CO2  in  this  gas  along  with  the  unusually 
low  oxygen  makes  .the  reactions  in  the  chambers  very  sluggish. 
In  order  to  get  reasonable  tonnage  from  the  plant  is  is  necessary 
to  use  much  more  than  the  normal  nitre  circulation  and  this  in 
turn  tends  to  make  high  nitre  loss. 

A  very  serious  feature  of  the  blast  furnace  work  is  the  irregu- 
larity of  the  gas  due  to  the  mode  of  operating  the  furnace.  It 
is  necessary  to  open  the  furnace  top  several  times  an  hour  to 
charge  and  barring  and  cleaning  are  necessary  every  day.  If 
the  flues  are  dampered  so  as  to  cause  some  pressure  at  the 
furnace  top,  the  working  conditions  on  the  charge  floor  are 


PRODUCTION  OF  SOZ  67 

almost  impossible.  If  suction  is  maintained,  every  time  the 
furnace  is  opened  false  air  rushes  in  and  dilutes  the  gas.  In 
spite  of  these  difficult  conditions  these  acid  plants  must  be 
considered  very  successful  both  technically  and  financially. 

COPPER  CONVERTERS 

It  has  many  times  been  suggested  that  the  gases  from  copper 
converters  might  be  used  for  making  acid,  but  as  yet  this  has 
not  been  attempted. 

Taken  without  modification  the  gas  from  a  single  converter 
ranges  in  a  period  of  a  few  hours  from  almost  no  S02  to  perhaps 
20  per  cent.  As  a  reasonable  approach  to  uniformity  is  a  neces- 
sity in  the  chamber  process,  such  a  gas  would  not  do.  It  may 
be  possible  with  a  battery  of  several  converters  working  on  a 
schedule  and  equipped  with  tight  hoods  and  dampers  to  get  a 
workable  gas.  It  must  be  said  that  the  converter  is  not  an 
attractive  source  of  gas  for  acid  making,  although  perhaps  a  not 
impossible  one. 

S02    FROM    ROASTING  ZINC  ORES 

In  the  reduction  of  the  sulfide  ores  of  zinc  it  is  necessary  to 
roast  off  sulphur,  and  the  gas  so  produced  is  utilized  in  making 
sulphuric  acid.  The  zinc  reduction  works  in  this  country  are 
usually  so  located  geographically  that  the  sulphuric  acid  produced 
is  readily  marketed. 

In  roasting  zinc  sulfide  ores  preliminary  to  distillation  for 
metal  it  is  necessary  to  convert,  as  nearly  as  possible,  all  the 
zinc  to  zinc  oxide.  In  order  to  do  this  certain  temperature  and 
oxygen  percentage  figures  must  be  observed  which  make  the 
roasting  operation  more  difficult  and  the  gas  less  favorable  for 
acid  making  than  in  roasting  pyrites. 

The  essentials  of  this  are  that  in  roasting  zinc  sulfide  some 
sulphates  of  zinc  form;  these  are  not  broken  up  completely  at 
temperatures  much  below  900°C.;  after  the  sulphur  content  of 
the  roasting  ore  is  down  to  about  8  per  cent  it  no  longer  burns 
with  sufficient  vigor  to  maintain  a  roasting  temperature,  much 
less  a  temperature  sufficient  to  break  up  the  sulphates.  It  is 
therefore  necessary  at  the  later  stages  of  the  roast  to  add  heat  by 
means  of  the  hot  gases  from  burning  carbonaceous  fuel.  As 
this  fire  gas  would  be  a  serious  diluent  of  the  roaster  gases  going 
to  the  chambers,  it  is  kept  separate  from  the  latter. 


68  AMERICAN  SULPHURIC  ACID  PRACTICE 

The  roasting  furnace  most  used  in  this  country  for  zinc  roasting 
in  connection  with  acid  chambers,  is  the  Hegler  furnace,  first 
used  at  the  Matthiesson  and  Hegler  works,  LaSalle,  111.  The 
Hegler  furnace  is  a  multiple  hearth,  rectangular  furnace,  with 
the  lower  hearths  of  muffle  construction.  The  ore  is  moved 
longitudinally  over  each  hearth  falling  to  the  one  below.  The 
rabbles  mounted  on  frames  of  steel  shapes  are  drawn  through 
the  hearths  by  means  of  long  rods.  After  each  passage  through, 
the  rabbles  are  drawn  clear  out  of  the  furnace  and  allowed  to 
cool  for  a  short  time.  Their  temperature  therefore  never 
becomes  high  enough  to  impair  their  strength  and  rigidity. 
The  latest  Hegler  furnaces  have  seven  hearths,  and  producer 
gas  is  used  to  heat  the  muffled  hearths  in  the  lower  parts  of  the 
furnace. 

In  order  to  properly  roast  zinc  ores  a  plentiful  supply  of  air 
must  be  allowed  to  pass  over  the  roasting  ore,  i.e.  the  oxygen 
percentage  must  be  kept  well  up.  Observing  this  requirement 
then,  the  gas  going  to  the  chambers  contains  only  4  to  5  per  cent 
S(>2.  There  is  of  course  some  dilution  due  to  rabbles  entering 
and  leaving  the  furnace  and  to  the  doors  leaking  air. 

BURNING  PYRITE  CINDER 

Even  with  the  most  careful  handling  some  where  about  2  to 
3  per  cent  of  sulphur  will  remain  in  the  cinder  from  roasting 
pyrites.  This  causes  two  losses,  that  of  the  sulphur,  and  that  of 
the  market  for  the  cinder  as  iron  blast  furnace  material,  as 
with  so  high  a  sulphur  content  good  iron  is  an  impossibility,  and 
many  acid  plants  have  a  potential  market  for  their  iron  "ore." 
The  Dwight  &  Lloyd  sintering  machine,  as  sold  by  the  American 
Ore  Reclamation  Co.,  71  Broadway,  New  York  City,  overcomes 
the  twin  difficulties  of  high  sulphur  content  and  fineness,  and  is 
best  described  by  the  company  as  follows: 

"  Sintering  is  a  comparatively  recent  art  in  the  iron  industry.  It  is 
the  process  of  agglomerating  fine  ore  material  into  a  mass  that  is  suit- 
able for  blast  furnace  use.  Sintering  may  be  illustrated  as  the  making 
of  flour  into  biscuits.  With  the  use  of  the  fine  ores  from  the  Mesaba 
Range  in  Minnesota  and  the  resulting  making  of  flue  dust  at  blast 
furnaces,  many  attempts  were  made  to  recover  the  valuable  iron  in  the 
flue  dust  by  briquetting.  This  means  of  treatment  has  not  proven  very 
satisfactory,  since,  to  secure  a  firm  bond,  the  process  is  expensive,  and 
when  the  bond  is  fickle  the  briquettes  quickly  return  to  dust. 


PRODUCTION  OF  S09  69 

"The  briquette  is  a  porous  mass  and  the  spaces  are  filled  with  air,  so 
that  the  mass  must  be  heated  first  to  expel  the  air  to  allow  the  reducing 
mass  of  the  furnace  to  come  in  contact  with  the  ore  particles,  which 
delays  the  reduction  and  the  mass  is  easily  disintegrated  into  dust. 
Sinter  made  by  the  continuous  down  draft  process  is  cellular  in  struc- 
ture, providing  an  open  and  large  area  of  contact  between  ore  and  reduc- 
ing gases;  and  as  the  cell  walls  are  quickly  heated  to  the  temperature 
required  for  reduction,  an  economy  in  coke  consumption  results  from 
the  use  of  sinter. 

"To  quote  Shinz's  law  (in  his  "Action  of  the  Blast  Furnace"):  'A 
chemical  action  can  only  take  place  between  two  bodies,  however  great 
their  affinity,  if  they  are  in  intimate  contact  with  each  other  and  the 
rapidity  of  this  action  will  be  much  greater  the  more  numerous  the 
points  of  contact  are.'  The  material  which  pro vides  the  greatest  area 
of  contact  is  more  readily  and  economically  reduced  in  the  furnace. 

"The  iron-bearing  materials  treated  by  sintering  include  blast-furnace 
flue  dust,  roll-scale,  magnetite  concentrates,  magnetic  sands,  high  sul- 
phur ore,  pyrites  cinder,  etc.  Any  finely  divided  ore  or  ores,  containing 
high  sulphur  or  high  moisture  and  combined  water,  can  be  converted 
into  ideal  material  for  use  in  the  blast  furnace.  Flue  dust  sludge  from 
blast-furnace  gas  washers  may  be  sintered  by  adding  the  sludge  to  a 
dry  sintering  mixture  instead  of  moistening  the  charge  with  water. 

"Sintering  was  first  applied  in  the  iron  industry  to  the  reclamation 
of  flue  dust,  but  it  has  since  widened  out  into  other  fields  and  demon- 
strated its  adaptability  for  treating  pyrites  cinder,  magnetic  ore  con- 
centrates, and  other  fine  ores  or  hydrated  ores. 

"A  plant  installation  is  made  up  of  two  main  parts,  the  sintering 
machine  proper,  and  the  raw  materials  plant,  both  forming  a  unit,  of 
which  the  former  is  more  or  less  standardized,  but  the  latter  made  to 
conform  to  local  conditions  and  materials.  The  following  is  a  descrip- 
tion of  a  typical  plant. 

"The  materials  to  be  sintered  are  delivered  to  a  series  of  bins,  the 
number  and  size  of  which  depend  on  the  kind  and  quantity  of  materials 
to  be  treated;  or  the  raw  materials  may  be  dumped  from  the  cars  into 
a  pit  and  transferred  to  the  bins  by  a  grab  bucket. 

"In  the  case  of  flue  dust  the  screening  of  it  is  necessary,  and  a  con- 
siderable quantity  of  coke  is  recovered  for  furnace  use. 

"The  bins  are  fitted  with  feeders  of  a  special  type  which  are  driven 
as  a  group  in  synchronism  with  the  sintering  machine.  The  required 
composition  of  the  sintering  mixture  is  made  up  by  adjusting  the  feeder 
gates  and  the  total  amount  of  sintering  mixture  delivered  by  the  feeders 
is  adjusted  to  suit  the  needs  of  the  sintering  machine  at  various  speeds. 
The  sintering  mixture  is  carried  to,  and  thoroughly  mixed  and  moistened 
in,  a  pug  mill  or  other  mixing  device,  and  is  delivered  onto  the  grates  of 
the  sintering  machine  in  a  continuous  layer  of  desired  thickness  and 


70 


AMERICAN  SULPHURIC  ACID  PRACTICE 


uniform  permeability.  This  continuous  layer  is  moved  under  an  igni- 
tion burner  where  the  fuel  in  the  upper  surface  of  the  layer  is  ignited 
and  the  charge  then  continues  its  movement  over  a  wind  box  connected 
to  a  suction  fan  which  draws  air  down  through  all  parts  of  the  charge 
and  the  sintering  action  is  progressive  through  the  whole  depth  of  the 
layer  down  to  the  grates.  At  the  end  of  the  sintering  machine  the 
sinter  is  discharged  over  a  grizzly  screem  which  thorouhly  separates 
all  fines  from  the  sintered  material  and  the  fine  sinter  is  returned  to  the 
sintering  machine  to  increase  the  permeability  and  thereby  the  rate  of 
sintering  is  increased." 

The  whole  operation  of  regulating  the  feeding  of  material  and 
speed  of  sintering  is  controlled  by  a  single  lever. 

SINTERING  MACHINES 

Capacities  of  the  three  machines  made  by  the  D wight  &  Lloyd 
people  are  as  follows,  all  in  tons  per  24  hours : 


Material 

Type  A 

Type  B 

TypeC 
(two  strand) 

Flue  dust 

125-150 

260-310 

550-650 

Pyrites  cinder.  .           

150-175 

300-375 

650-750 

Magnetic  concts 

175-200 

350-400 

750-900 

Pyrites  cinder  and  high  sulphur  ores  are  sintered  and  desul- 
phurized in  one  operation.  The  cinder  contains  from  1.5  per 
cent  to  5  per  cent  sulphur,  and  is  reduced  to  0.10  per  cent  to 
0.15  per  cent  in  the  sintered  product.  About  8  to  10  per  cent 
fuel  is  required. 


CONTENTS 


Iron 

Sulphur. . . 


PYRITES  CINDER, 

PER  CENT 

.       56.28 
4.41 


SINTER, 

PER  CENT 

61.00 
0.07 


MIXTURE  OF  PYRITES  CINDER  AND  FLUE  DUST 


Contents 

Pyrites 
cinder, 
per  cent 

Flue  dust, 
per  cent 

Average 
mixture, 
per  cent 

Sinter 

Iron                  

56.28 

33.00 

46  97 

57  10 

Sulphur 

4  41 

0.18 

2  72 

0  12 

Carbon 

24  00 

9  60 

PRODUCTION  OF  SO, 


71 


72 


AMERICAN  SULPHURIC  ACID  PRACTICE 


PRODUCTION  OF  SOZ 


73 


74 


AMERICAN  SULPHURIC  ACID  PRACTICE 


PRODUCTION  OF  SOZ  75 

Sintering  machines  of  this  type  are  also  used  to  treat  lead  ores 
as  a  preparation  for  blast  furnacing. 

The  gas  from  a  sintering  machine  is  not  only  low  in  SO2,but 
as  it  is  high  in  CO2  and  CO,  it  is  not  good  acid  material.  SO2  has 
been  hard  to  concentrate  up  to  recent  years,  but  a  new  process 
is  now  on  the  market  which  makes  available  very  weak  gases. 

Silica  gel  is  put  out  by  the  Davison  Chemical  Co.  at  Baltimore. 
While  this  material  has  been  known  for  years,  its  commercial 
production  was  not  possible  until  the  researches  of  Prof.  W.  A. 
Patrick  of  Johns  Hopkins,  on  gas  mask  absorbers  during  the  war. 
Apparently  any  condensible  gas  is  adsorbed  by  this  material, 
the  capacity  of  which  is  very  great,  and  a  small  rise  in  tempera- 
ture serves  to  drive  out  the  adsorbed  gas.  This  is  so  much  the 
case  that  the  additional  gas  pressure  produced  by  the  slight 
increase  in  temperature  caused  by  laying  ones  hand  on  the 
apparatus  is  easily  measured. 

The  action  is  unquestionably  surface  condensation,  the  small 
drops  of  "gel"  being  full  of  sub-microscopic  cracks,  so  that  Prof. 
Patrick  says,  "if  you  consider  the  measure  of  the  'gel'  drop  in 
centimeters,  you  must  measure  the  area  of  the  cracks  in  acres." 

This  plant  consists  of  three  towers  in  series,  each  capable  of 
being  cut  out.  Only  one  is  used  at  a  time,  one  being  discharged 
and  the  third  in  reserve.  The  temperature  is  raised  or  lowered 
by  forcing  steam  or  brine  through  horizontal  pipes  laid  in  the  gel 
mass.  Vertical  pipes  were  tried,  but  the  channeling  action  of 
the  gas  was  too  great.  This  opens  up  a.  new  type  of  contact 
plant  where  the  concentration  of  SO2  in  the  gas  can  be  very  high, 
thus  cutting  down  plant  and  particularly  mass,  very  greatly. 
The  advantage  of  being  able  to  mix  air  and  SO2  instead  of  air 
and  sulphur,  is  at  once  apparent.  When  sulphur  is  burned  in  air 
and  that  mixture  taken  into  the  system,  the  nitrogen  that  was 
in  the  air,  the  oxygen  of  which  helped  form  the  SO2  goes  along 
and  dilutes  the  gas,  whereas  by  having  the  SO2  ready  burned, 
that  dead  gas  is  avoided. 

If  there  is  sufficient  oxygen  present,  the  contact  mass  is  more 
efficient  as  the  concentration  of  the  gas  increases.  By  sufficient 
oxygen  is  meant  the  excess  that  is  needed  to  give  good  results. 
So  the  use  of  a  gas  mixture  made  from  SO2  direct  works  out  as 
follows :  In  a  gas  made  by  burning  sulphur  in  the  air  and  contain- 
ing 7  per  cent  S02,  12.3  per  cent  of  the  total  is  the  nitrogen  that 
accompanied  the  3.5  per  cent  oxygen  necessary  to  make  the 


76  AMERICAN  SULPHURIC  ACID  PRACTICE 

SO2.  This  concentration  process  reduces  the  amount  of  gas 
to  be  handled,  raises  the  concentration  of  the  gas,  and  leaves 
just  as  much  oxygen  to  form  SOs  and  furnish  the  excess  necessary 
for  this  formation. 

Silica  gel  should  be  tried  out  along  the  following  lines,  as  the 
concentration  of  platinum  in  the  mass  drops  the  conversion 
drops,  also,  but  not  in  the  same  proportion.  Therefore,  there 
is  a  point,  to  be  determined,  to  which  it  will  pay  to  drop  the 
conversion,  catching  the  unconverted  SOa  with  silica  gel,  and 
returning  it  to  the  gas  stream. 

The  saving  will  be  in  plant  cost  of  platinum.  Suppose  that 
with  10  per  cent  of  the  amount  of  platinum  required  for  a  97 
per  cent  conversion  you  are  able  to  get  a  60  per  cent  conversion 
and  recover  the  SO2  at  reasonable  expense.  At  the  standard 
rate  of  platinum  used,  for  a  plant  burning  one  ton  of  brimstone 
an  hour,  90  pounds  avoirdupois,  of  platinum  would  be  required. 
At  $95  an  ounce,  troy,  that  is  $1,385  a  pound  avoirdupois  or, 
$124,650  for  platinum.  Ten  per  cent  of  that  would  be  $12,465, 
quite  a  difference. 

Without  anywhere  near  sufficient  research  work  done  upon 
this  subject,  I  do  not  state  the  above  as  either  an  accomplished 
fact,  nor  as  a  certainty — it  is  simply  a  possible  lead.  The 
Davison  Chemical  Co.,  Baltimore,  Maryland,  hold  the  basic 
patents  on  silica  gel,  and  will  furnish  the  most  complete  informa- 
tion upon  this  subject  that  exists. 

Water  is  an  obstacle  to  the  adsorption  by  silica  gel,  as  it  is  a 
great  moisture  adsorber,  and  the  moisture  would  be  given  up, 
under  certain  conditions,  along  with  the  SC>2,  which  would  have 
to  be  dried  again  before  conversion.  Of  course  there  would 
be  no  moisture  in  the  gas  just  leaving  the  strong  acid  of  the 
absorption  towers. 

When  the  contact  process  first  became  an  accomplished  fact 
many  people  looked  for  it  to  displace  chambers  entirely,  but  the 
cost  of  the  platinum  required  has  prevented  the  fulfilment  of 
their  hopes.  Is  it  too  much  to  hope  that  silica  gel  may  bring 
this  about? 

OTHER  USES  OF  SO2 

Liquid  S02  was  first  made  commercially  from  zinc  smelter 
gases  in  this  country  by  the  Davison  Chemical  Co.  in  Baltimore 
around  1870.  It  is  interesting  to  note  that  the  first  sulphite 


PRODUCTION  OF  SO2  77 

» 

paper  pulp  in  this  country  was  made  with  liquid  S02  by  the 
Mitcherlich  process,  then  the  pulp  mills  began  to  burn  their  own 
sulphur,  and  now  the  pendulum  has  swung  back  again. 

For  liquid  SO2  the  normal  boiling  point  is —  11°C. 

For  liquid  SO2  the  latent  heat  of  vaporization,  at  —  10°C.  (dimin- 
ishes as  the  temperature  rises) 93 . 4  cal. 

Vapor  pressure  temp.  C....    -10        0          10         20         30         40         50 
Pressure  (atmospheres) 1.0     1.53     2.26     3.24     4.51     6.15     8.18 

Critical  temperature  =  155°C.     Critical  pressure  =  78.9  atmospheres. 
Specific    heat,  between  -  20°  and  +  130°C.  =  0.31712  +  0.0003507*  + 
0.00000672^ 

ACTION  OF  METALS 

The  commercial  product,  containing  0.07  per  cent  H20,  attacks 
iron  above  70°C.,  forming  a  solid  crust  of  ferrous  sulphate  and 
thio-sulphate,  but  the  metal  is  not  further  attacked.  Anhydrous 
S02  does  not  attack  either  iron  or  steel. 

USES 

For  refrigeration,  because  of  its  cheapness,  ease  of  handling, 
and  the  fact  that  it  is  neither  acid  nor  alkalin  in  its  action. 

In  the  manufacture  of  sulphite  pulp. 

For  petroleum  refining. 

As  a  solvent  for  organic  fats  and  resins. 

As  a  sewage  disposal  agent. 

So  far  as  I  know,  there  are  three  plants  in  this  country  making 
liquid  SO2.  The  Tacoma  Smelter,  of  the  American  Smelting 
and  Refining  Co.,  Tacoma,  Wash.,  has  a  plant  that  has  been  in 
operation  about  5  years, — operating  as  follows :  The  gas  from  the 
converters,  containing  2.5  per  cent  to  3  per  cent  SO2,  and  at  about 
300°C.,  is  lead  to  a  scrubber  tower,  brick  lined  and  loose  brick 
packed,  into  the  top  of  which  is  fed  a  small  amount  of  water,  just 
enough  to  prevent  it  all  vaporizing.  The  run  off  cleans  the  gas,  but 
because  of  its  temperature  contains  practically  ho  SO2.  The 
gas  then  goes  to  another  tower,  of  the  same  construction,  but 
larger  in  diameter,  to  which  water  is  admitted  through  spray 
nozzles  at  the  top,  the  water  being  in  sufficient  quantity  to  cool 
down  and  absorb  practically  all  the  SO2,  the  scrubbed  gases 
going  out  the  stack.  See  Fig.  11. 

The  liquor  flows  by  gravity  to  a  heat  exchanger,  made  of 
lead  pipe,  outside  of  which  flows  the  desulphurized  liquors, 


78 


AMERICAN  SULPHURIC  ACID  PRACTICE 


hot,  from  the  following  process.  Then  to  12-in.  lead  pipes, 
horizontal,  into  the  bottom  of  which  is  blown  steam,  which 
vaporizes  the  S02,  which  comes  off  through  a  gas  outlet  on  top, 
and  thence  to  the  compressor.  The  water,  after  the  SO 2  has 
been  blown  off,  flows  down  to  heat  the  heat  exchanger. 

Before  the  compressor  is  a  scrubber,  fed  with  66°Be*.  acid,  to 
remove  moisture  from  the  SO2.  This  66°  acid  drops  to  60°  in  a 
week,  and  has  to  be  renewed. 

The  compressor  is  a  bronze,  single-stage,  direct-driven  one, 
compressing  to  about  60  lb.,  although  under  perfect  conditions 
45  lb.  will  do  it.  The  liquid  SC>2  then  goes  to  lead  cooling  coils, 
over  which  water  drops,  and  thence  to  a  tank  car. 

An  iron  cylinder  for  the  compressor  only  lasts  six  weeks. 


FIG.  11. 

The  storage  tank,  built  to  stand  300  lb.,  has  a  safety  valve 
with  a  pipe  running  to  the  absorber  tower,  where  any  SO2  will 
be  caught  and  the  non-condensible  gases  will  escape  to  the  stack. 

This  plant  started  to  produce  in  1917,  making  10  tons  of  liquid 
S02  per  day.  In  1920  the  production  was  increased  to  30  tons 
per  day,  and  in  1921  it  will  be  50  tons.  The  product  is  shipped 
partly  to  Crown  Willimette,  where  it  is  combined  with  SC>2 
produced  on  the  ground,  to  make  a  25  per  cent  gas  to  make  a 
strong  cooking  liquor  for  making  sulphite  pulp.  The  rest  of  the 
production  goes  to  Los  Angeles  for  oil  refining^ 

At  Tacoma,  with  coal  at  $8,  SO2  from  a  3  per  cent  gas,  includ- 
ing overhead,  but  with  no  charge  for  the  gas,  is  (1920)  $8  per  ton. 

The  plant  of  the  Virginia  Smelting  Co.,  at  Norfolk,  Va.,  has 

Without  steam  or  power  plant,  a  10-ton  per  day  plant  costs  (1920)  $30,000. 
Without  steam  or  power  plant,  a  30- ton  per  day  plant  costs  (1920)  $45,000. 


PRODUCTION  OF  SO*  79 

been  leased  to  Beer,  Sondheimer,  &  Co.,  who  are  recovering  the 
SO2  in  a  process  very  similar  to  the  one  at  Tacoma,  except 
that  it  is  much  smaller,  and  the  liquid  S02  is  shipped  in  cylinders. 

There  is  a  small  plant  in  Wisconsin  which  produces  SO2  from 
brimstone  directly  for  the  purpose  of  compressing  and  selling. 
I  have  been  unable  to  get  any  details. 

Dr.  Ralph  McKee,  head  of  the  Department  of  Chemical 
Engineering  at  Columbia,  is  a  world's  authority  on  liquid  SO2. 
He  has  furnished  some  of  the  information  contained  in  this 
section,  and  sees  a  great  future  for  the  industry,  some  of  the 
reasons  for  which  are  given  below. 

Liquid  SO2  will  not  burn  nor  explode,  will  not  attack  steel 
containers,  and  costs  %i  a  pound,  F.O.B.  point  of  manufacture, 
against  7ff  for  gasoline  and  15  ff  for  carbon-tetrachloride  (1920). 

The  U.  S.  Bureau  of  Chemistry  does  not  like  the  use  of  liquid 
SO2  for  the  extraction  of  oils  to  be  used  for  food,  if  any  other 
solvent  can  be  used. 

Mr.  James  E.  Steely,  of  the  West  Virginia  Pulp  and  Paper 
Company,  Inc.,  has  furnished  some  notes  on  the  production  and 
use  of  SO2  in  the  pulp  industry. 

In  the  manufacture  of  bi-sulphate  liquor,  it  is  desirable  to  have 

502  gas  at  as  high  a  percentage  as  possible,  as  the  solubility  of  the 
gas.  in  water  increases  in  the  per  cent  of  SO2  in  the  gas.     This 
solubility  also  increases  with  a  reduction  in  temperature;  there- 
fore the  gas  is  cooled  as  low  as  possible,  usually  in  some  form  of 
lead-pipe  cooler. 

It  is  also  necessary  to  keep  the  SO3  in  the  gas  as  low  as  possible, 

503  being  a  very  undesirable  component  of  gas  for  sulphite  pulp 
manufacture. 

A 15  per  cent  to  18  per  cent  S02  gas  meets  the  above  requirements. 
Liquid  SO2  is  a  most  desirable  material  to  work  with,  and  if  it  could 
be  delivered  at  the  mill  at  slightly  above  the  cost  per  pound  of 
sulphur,  as  compared  to  elemental  sulphur,  it  would  be  in  very 
wide  demand.  However,  under  present  (1920)  conditions,  the 
cost  of  .producing  liquid  SO2  together  with  increased  cost  of 
freight  and  containers  for  handling  would  make  the  proposition 
prohibitive  in  ordinary  times.  The  efficiency  of  operation  in  a 
sulphite  acid  plant  is  very  high,  and  maintainance  cost  of  first- 
class  equipment  comparatively  low;  therefore  it  would  seem  that 
only  in  special  cases  would  liquid  S02  be  attractive  to  sulphite 
pulp  manufacturers. 


80  AMERICAN  SULPHURIC  ACID  PRACTICE 

The  chief  source  of  SO2  for  sulphite  pulp  manufacture  is  ele- 
mental sulphur,  burned  in  the  same  types  of  burner  that  are  used 
in  acid  manufacture.  Very  little  SO3  is  produced  by  any  of  these 
machines,  but  to  make  assurance  doubly  sure,  at  some  plants  a 
pyrometer  is  installed  in  the  combustion  chamber  and  the  tem- 
perature maintained  around  1500°F.,  at  which  point  SOs  disso- 
ciates into  SO2  and  O.  Other  plants  depend  solely  upon  gas 
analyses. 

Pyrites,  particularly  from  Spain,  used  to  be  the  chief  source  of 
SO2  for  pulp  making,  but  the  Louisiana  sulphur  discoveries,  and 
the  interruption  to  Spanish  deliveries  by  the  War,  cut  down  its 
use  so  that  today  (1920)  Mr.  Steely  does  not  know  a  single  plant 
in  this  country  running  on  pyrites.  The  market  price  of  Spanish 
pyrites  has  not  gone  low  enough  to  justify  plants  that  used  to  use 
it  returning,  and  also  most  important,  the  burners,  usually  of  the 
Herreshoff  or  Wedge  type,  must  be  operated  with  the  greatest 
care  to  prevent  formation  of  SO3,  due  to  the  catalytic  action  of  the 
hot  iron  oxides  in  the  cinders. 

There  are  two  general  schemes  for  making  bi-sulphite  liquor. 
In  each  case  the  S02  is  cooled  as  low  as  possible.  The  first 
scheme  is  to  use  a  tall  tower  filled  with  lumps  of  lime  stone,  over 
which  a  slow  stream  of  water  is  passing.  The  gas  is  admitted  to 
the  bottom  of  the  tower,  and  is  absorbed  by  the  waterr  forming 
sulphurous  acid,  which  in  turn  dissolves  the  stone  to  make 
calcium-bi-sulphate  liquor.  i 

The  second  scheme  consists  of  passing  the  gas  through  towers 
containing  a  solution  of  milk  of  lime.  The  two  are  brought 
together  in  such  a  way  that  they  combine  and  form  a  clear 
solution  of  bi-sulphite. 

When  rosin  is  extracted  from  yellow  pine  waste,  enough  S02 
remains  in  the  wood  to  cook  the  pulp.  Both  United  States  and 
Canadian  patents  on  this  process  are  applied  for  by  Ralph 
McKee  and  A.  A.  Holmes. 

The  city  of  New  Haven  has  experimented  with  liquid  S02 
on  sewage  disposal.  The  sewage  was  going  into  the  bay;  if  an 
acid  was  added  the  colloidal  sludge  was  precipitated.  H2SC>4 
was  first  used,  then  S02.  If  this  sludge  is  dried  and  extracted, 
considerable  amounts  of  fats  and  oils  are  recovered,  gasoline 
being  used  as  the  solvent.  The  report  says  the  recovery  will 
pay  costs,  including  bond  interest. 

Liquid  S02  is  a  solvent  for  di-ethylamine,  analine,  di-phenyl- 


f  r  PRODUCTION  OF  SO,  .  81 

amine,  benzylamine,  P-toluidine,  A-naphthylamine,  B-naphthyl- 
amine,  phenyl,  B-naphthylamine,  benzidine,  chrysaniline, 
carbazol,  quinolin,  pyridine,  acetanilide,  acetnaphtalid,  benzene, 
toluene,  tri-phenyl-methane,  di-phenyl-flouren,  phenanthren, 
naphthalene,  nitrobenzene,  limonen,  pinene,  anthracene,  B-di- 
bromnaphthalene.  All  fatty  alcohols  from  methyl  to  capryl, 
benzyl  alcohol,  menthol,  borneol,  O-cresol,  B-naphthol,  hydro- 
quinone,  picric  acid,  phenol-chloro  (and  di-chloro)  acetic  acid, 
A-brom-butyric  acid,  benzoic  acid,  salicylic  acid,  M-oxybenzoic 
acid,  B-naphthoic  acid,  acetic-ethyl-ester,  succionic-acid-di- 
ethyl-ester,  asopropyl-aceto-acetic-ester,  fumaric-acid-di-ethyl- 
ester,  cinnamic-acid-di-ethyl-ester,  malic-acid-di-methyl-ester, 
mandelic-acid-di-ethyl-ester,  acetic-acid-bornyl-ester,  ricanelic- 
acid-propyl-ester. 

The  following  are  also  soluble — KI,  Nal,  NH3I,  Rul,  tri-methyl- 
sulphoneum-iodide,  tri-methyl-ammonium,-iodide,  KBr,  ammo- 
nium-thio-cyanate,  methyl-ammonium-chloride,  di-,  tri,  and 
tetra-methyl-ammonium-bromide,  sublimed  ferric  chloride,  co- 
balt-thio-cyanate.  More  compounds  for  which  liquid  SC>2  is  a 
solvent  are  continually  being  discovered. 

CANADIAN  SITUATION 

Dr.  McKee  shows  a  picture  of  the  smelter  of  the  International 
Nickel  Co.,  with  clouds  of  SO2  coming  out  of  the  stack — 1,000  tons 
a  day.  There  are  numerous  copper,  nickel,  and  zinc  smelters 
in  the  Dominion,  and  the  large  pulp  mills  near  at  hand  are  import- 
ing sulphur  from  Louisiana  and  Japan,  while  this  S02  is  worse 
than  thrown  away — it  is  acutally  hurting  the  nearby  farms. 

The  Tennessee  Copper  Co.  showed  that  the  production  of  acid 
from  smelter  fume  was  not  an  impracticable  dream,  and  when  the 
acid  was  produced  a  market  was  found  for  it.  The  method  of 
producing  liquid  S02  from  smelter  fumes  is  already  in  successful 
operation,  and  the  market  for  the  product  is  ready  and  waiting 
at  the  door. 


CHAPTER   VI 
A  BRIEF  DESCRIPTION  OF  THE  CHAMBER  PROCESS 

The  Chamber  Process  for  the  manufacture  of  sulphuric  acid 
takes  its  name  from  the  lead  chambers  which  constitute  the 
chief  essential  part  of  the  apparatus.  It  differs  from  the  other 
important  process  of  making  sulphuric  acid,  the  contact  process, 
both  in  nature  of  the  plant  proper  and  in  the  chemical  reactions 
involved.  The  purpose  of  each  is  to  oxidize  S02  up  to  H2SO4. 
The  chamber  process  does  this  by  means  of  the  reactions  between 
SO2,  the  higher  oxides  of  nitrogen,  oxygen,  and  water,  at  low  tem- 
peratures, while  the  oxidation  in  the  contact  process  is  accom- 
plished by  a  catalyzer,  usually  finely  divided  platinum,  at  a 
comparatively  high  temperature. 

The  normal  product  of  chamber  plants  is  sulphuric  acid  of  50° 
to  60°Be.  Contact  plants  normally  produce  acid  of  98  per  cent 
H2SO4  or  higher  strengths.  The  chamber  process  makes  50°  to 
60°  acid  more  cheaply  than  the  contact  process  can  make  acid 
of  that  grade.  The  chamber  process  cannot,  however,  make  high- 
strength  acid.  Each  process  therefore  has  its  distinct  field. 

The  essential  parts  of  a  modern  chamber  plant  are : 

1.  Burners  of  some  kind  for  the  production  of  SO2. 

2.  Dust  settling  apparatus,  except  in  those  cases  where  brimstone  is 
burned  to  make  SO2. 

3.  Glover  Tower. 

4.  Chambers. 

5.  Gay  Lussac  Towers. 

6.  Acid  Circulating  Apparatus. 

7.  Fans  and  flues. 

8.  Apparatus  for  introducing  the  oxides  of  nitrogen. 

The  gas  produced  in  the  burners  is  derived  from  the  oxidation 
of  elemental  sulphur,  iron  sulfide,  iron-copper  sulfides,  zinc  sulfide 
or  mixed  sulfides.  It  contains  from  5  per  cent  to  10  per  cent 
SO2,  depending  on  the  material  burned,  8  per  cent  to  12  per  cent 
oxygen,  and  nitrogen,  with,  in  special  cases  some  C02  or  possibly 

CO. 

82 


A  BRIEF  DESCRIPTION  OF  THE  .CHAMBER  PROCESS     83 

When  necessary  this  gas  is  drawn  through  some  form  of  dust- 
settling  apparatus  to  remove  the  greater  part  of  the  dust  which 
would  otherwise  contaminate  the  acid. 

If  nitre  potting  is  practiced,  the  gas  next  passes  around  the 
nitre  pots.  These  are  cast  iron  vessels  set  in  the  gas  flue,  into 
which  are  introduced  nitrate  of  soda  and  sulphuric  acid.  The 
hot  gases  cause  these  compounds  to  react  to  form  nitric  acid 
vapor,  and  a  mixture  of  sodium  sulphate  and  sodium  bisulphate. 
The  latter  is  tapped  off  molten,  at  intervals.  The  nitric  acid 
vapor  is  reduced  to  NO  by  the  hot  S02  and  is  carried  along  with 
the  gas. 

The  gas  mixture  next  enters  the  Glover  tower  at  a  temperature 
of  800°F.  to  1,000°F.  It  is  in  this  tower  brought  into  intimate 
contact  with  a  mixture  of  60° Be*,  sulphuric  acid  carrying  in 
solution  N20s,  and  chamber  acid  of  about  50°  Be*.  The  hot  gas 
with  its  considerable  SO2  content,  reacts  with  the  acid  and  de- 
nitrates  it  or  removes  from  it  its  N2O3,  forming  some  H2SO4  and 
converting  practically  all  the  N2Os  into  NO,  a  gas,  which  goes 
on  with  the  main  gas  stream.  Steam  and  some  weak  sulphuric 
acid  vapor  are  also  formed  and  go  on  with  the  gas.  Leaving  the 
Glover  tower  the  gas  mixture  contains  then  a  somewhat  reduced 
percentage  of  SO2,  nitric  oxide  (NO),  oxygen,  nitrogen  and  steam 
or  weak  acid  vapor.  Its  temperature  has  been  reduced  to 
about  200°F. 

If  nitre  potting  is  not  practiced  it  is  customary  to  introduce 
some  fresh  nitric  acid  into  the  Glover  tower  top. 

The  acid  issuing  from  the  Glover  tower  at  the  bottom  is 
maintained  at  a  gravity  of  about  60°  Be*.  It  has  a  temperature 
of  200°F.-300°F.  and  is  passed  through  a  cooling  system  con- 
sisting of  a  tank  containing  lead  pipe  coils  through  which  cold 
water  is  circulated.  The  acid  should  leave  this  cooler  at  as  low 
a  temperature  as  possible,  certainly  not  over  80°F.  A  part 
of  this  acid  is  elevated  and  introduced  into  the  Gay  Lussac  towers, 
and  the  remainder  is  shipped. 

The  gas  mixture  from  the  Glover  tower  is  conducted  into  the 
chambers,  usually  from  3  to  10  in  number,  in  series.  From  1  to 
2  hrs.  is  occupied  by  any  given  portion  of  the  gas  in  passing 
through  the  set  of  chambers.  Steam  or  atomized  water  is 
introduced  at  various  points.  By  the  reactions  between  SO2, 
oxygen,  the  oxides  of  nitrogen  and  water,  sulphuric  acid  is 
formed.  This  collects  in  the  bottoms  or  pans  of  the  chambers. 


84 


AMERICAN  SULPHURIC  ACID  PRACTICE 


When  these  reactions  have  gone  on  for  the  proper  period  of 
time  and  the  gas  finally  reaches  the  end  of  the  last  chamber  the 
SO2  percentage  has  been  reduced  to  less  than  ^{Q  of  1  per  cent, 
and  the  nitrogen  oxides  are  practically  all  in  the  form  of  N2O3. 
It  is  highly  important  that  the  SO2  percentage  be  reduced  below 
Jf  o  °f  1  per  cent  or  else  the  recovery  of  the  nitrogen  compounds 

Rcasters 


Dust  Chamber 
O-f-N  to  Atmosphere 


Chambers v 


Wb^ 

D 

~jf  —  2H2S04+N203  *HSN0S+H20 

\     |     lA-/ 

|||    Coo/c 

1 

H» 

n7 

,\  ^/-/^//^^//^^//^^^c? 

£ 

0 
H 

\N203+2S02+2O+H20=2H$h 

H20ct5  spray  or  steam  is 
introduced  info  chambers 

at  many  prints 

c 

\ 

V- 

* 

+30+H20 
2HSH05  +H20  =  Z 

FIG.   12.— Flow  Sheet  of  Chamber  Process. 

will  be  incomplete.  It  is  almost  as  essential  that  the  SO2  per- 
centage be  not  less  than  £f  oo  of  1  per  cent  for  the  same  reason, 
and  also  because  of  increased  corrosion  of  the  lead.  These 
points  will  be  taken  up  in  more  detail  later  on. 

By  properly  regulating  the  amount  of  water  or  steam  intro- 
duced the  acid  made  in  the  chambers  is  kept  at  approximately 
50°Be*.  It  is  not  permissible  to  allow  the  continued  formation  of 
acid  of  much  greater  concentration  because  of  the  tendency  of 


A  BRIEF  DESCRIPTION  OF  THE  CHAMBER  PROCESS      85 

such  acid  to  take  into  solution  some  of  the  oxides  of  nitrogen,  in 
which  case  they  are  no  longer  available  for  reaction  with  SO2. 

The  acid-making  reactions  generate  a  large  amount  of  heat 
which  is  carried  off  mostly  by  radiation  from  the  lead  chamber 
walls.  The  chambers  should  therefore  be  housed  in  a  well- 
ventilated  building. 

From  the  chambers  the  gases  pass  into  the  Gay  Lussac  towers. 
Their  function  is  to  recover  the  N2Os.  This  is  accomplished  by 
bringing  the  gas  into  intimate  contact  with  cold  60°  Be",  sulphuric, 
acid,  which  takes  85  per  cent  to  90  per  cent  of  the  N2Os  into 
solution,  forming  what  is  known  as  nitrous  vitriol.  Perfect 
recovery  of  the  N203  is  never  attained  because  the  cost  of  appara- 
tus to  accomplish  it  is  prohibitive. 

The  gas  which  leaves  the  Gay  Lussac  towers  consists  of  94  to 
96  per  cent  nitrogen,  4  to  6  per  cent  oxygen  with  traces  of  other 
things.  It  is  discharged  into  the  atmosphere  through  a  stack. 

The  acid  issuing  from  the  Gay  Lussacs,  carrying  usually  from 
1  per  cent  to  2  per  cent  N2C>3,  is  elevated  to  the  top  of  the  Glover 
tower  and  the  N20a  there  reintroduced  into  the  system. 

Figure  12  shows  a  conventional  plan  of  a  chamber  plant  and 
indicates  the  reactions  which  occur  in  the  various  parts  of  the 
apparatus. 


CHAPTER  VII 
DUST  SETTLING  APPARATUS 

A  chamber  acid  plant  will  usually  require  some  provision  for 
removing  dust  from  the  burner  gases.  This  varies  from  almost 
nothing  in  the  case  of  brimstone  burners,  to  rather  large  and 
elaborate  chambers  for  use  when  very  fine  sulphide  ore  is  burned. 
It  is  highly  important  in  order  to  insure  uninterrupted  operation 
to  provide  suitable  and  adequate  means  for  dust  removal.  If 
any  considerable  amount  of  dust  is  carried  into  the  Glover  tower 
by  the  gas  it  causes  the  following  disagreeable  and  serious  results : 
The  packing  of  the  Glover  tower  will  become  obstructed,  inter- 
fering with  passage  of  the  gas.  The  acid  will  be  contaminated 
and  rendered  impure.  Even  though  this  may  not  be  of  impor- 
tance to  the  consumer  of  the  acid,  it  will  cause  gradual  fouling  and 
obstruction  of  pipes,  valves,  tanks  etc.,  in  the  acid  plant  and  will 
make  uniform  running  impossible. 

There  are  two  general  principles  applied  in  dust  removal,  which 
are:  decreasing  gas  velocity,  and  causing  change  of  direction  of 
the  gas  stream.  It  is  hardly  necessary  to  consider  some  of  the 
older  proposals  for  washing  the  gas  by  water  or  acid,  as  these 
involve  cooling  the  gas  so  much  that  the  Glover  tower  will  not 
function  properly.  In  general,  it  is  necessary  to  retain  the  tem- 
perature of  the  gases  as  high  as  possible  from  the  furnaces  to  the 
Glover  tower.  Dust  chambers  for  acid  plants  should  therefore 
be  compact  and  well  insulated. 

The  Cottrell  apparatus  has  been  used  in  a  few  acid  plants 
with  considerable  success.  It  probably  has  a  distinct  place 
in  acid  plant  design  when  the  sulphur  bearing  material  burned 
produces  very  fine  dust.  This  form  of  treater  is  hardly  justi- 
fied otherwise,  as  it  is  expensive  to  install,  and  involves  some 
operating  expense.  The  following  information  is  furnished  by 
the  Research  Corporation,  31  West  43rd  St.,  New  York: 

COTTRELL  PRECIPITATORS  FOR  CLEANING  ROASTER  GASES 

The  problem  of  satisfactorily  cleaning  the  sulphur  dioxide  gases  prior 
to  their  oxidation  and  conversion  into  sulphuric  acid  has  long  been  a 

86 


DUST  SETTLING  APPARATUS 


87 


troublesome  one  for  acid  makers  to  solve.  In  contact  acid  plants  it  is 
of  course  essential  that  the  gases  be  completely  freed  from  suspended 
particles  of  dust  or  fume  prior  to  their  passage  through  the  catalyst 
and  it  is  almost  equally  desirable  in  the  case  of  chamber  plants  that  the 
sulphur  dioxide  gases  be  thoroughly  cleaned  if  the  plant  is  to  operate 
at  high  efficiency  and  produce  a  clean  acid  of  good  quality.  In  the 
latter  case,  however,  the  problem  is  complicated  by  the  fact  that  the 
sulphur  dioxide  gases  must  be  cleaned  at  a  very  high  temperature 
whereas  in  contact  plants  the  gases  may  be  cooled  during  the  cleaning 
process  or  may  be  cooled  first  and  then  purified. 


FIG.  13. 

In  both  cases  the  Cottrell  Processes  of  Electrical  Precipitation  offer 
a  very  satisfactory  method  of  cleaning  the  gases,  and  several  Precipita- 
tion Installations  are  today  in  use  for  such  purposes. 

In  designing  Cottrell  Precipitators  for  cleaning  roaster  gases  the 
temperature  at  which  the  gases  must  be  cleaned  and  the  character  of 
the  suspended  matter  to  be  removed  from  such  gases  are  governing 
factors.  Of  course  the  size  of  the  installation  depends  directly  upon 
the  volume  of  gas  to  be  cleaned  and  this  in  turn  is  fixed  by  the  quantity 
of  material  being  roasted  per  unit  of  time  and  by  its  sulphur  content 
as  well  as  by  the  percentage  of  sulphur  dioxide  in  the  gases  leaving  the 


88 


AMERICAN  SULPHURIC  ACID  PRACTICE 


furnaces.  These  factors  must  therefore  be  known  or  approximated  in 
order  that  a  precipitation  plant  of  suitable  capacity  may  be  provided. 
Two  types  of  precipitators  are  today  being  installed  for  cleaning  the 
hot  furnace  gases  in  sulphuric  acid  plants.  These  types  differ  widely 
from  each  other  and  the  decision  as  to  which  type  should  be  installed 
is  based  largely  upon  the  temperature  and  fume  or  dust  conditions  in 
the  particular  plant  under  consideration.  In  cases  where  the  gases 
must  be  cleaned  at  temperatures  of  1,000°F.  and  over  and  where  the 
suspended  matter  to  be  removed  is  mostly  dust  rather  than  fume,  pre- 


FIG.   14. 

cipitators  of  the  so-called  plate  type,  in  which  the  gases  pass  horizontally 
between  the  collecting  and  discharge  electrodes,  have  proven  highly 
satisfactory.  On  the  other  hand,  where  the  gases  can  be  cooled  to  a 
temperature  of  about  600°F.  or  under  before  cleaning  and  where  the 
suspended  matter  to  be  removed  is  fume  rather  than  dust,  precipitators 
of  the  pipe  type,  in  which  the  gases  pass  upwards  between  the  collecting 
and  discharge  electrodes,  would  in  general  be  the  more  suitable. 

Figure  14  is  a  photograph  of  a  Cottrell  Precipitator  of  the  pipe  type 
which  was  recently  installed  under  the  supervision  of  the  Research 
Corporation  at  a  plant  in  Wisconsin.  Here  17,500  cubic  feet  of  gas 


DUST  SETTLING  APPARATUS 


89 


per  minute  at  a  temperature  of  500°F.  are  cleaned.  These  gases  come 
from  three  Mathey  rotary  kilns  roasting  Wisconsin  zinc  ore  concentrates, 
and  after  being  cleaned  are  used  for  the  manufacture  of  sulphuric  acid 
by  the  contact  method.  The  precipitator  as  installed  consists  of  two 
units,  each  having  36  collecting  electrode  tubes  or  pipes.  These  pipes 
are  of  steel,  12  in.  in  diameter  and  15  ft.  in  height.  Means  are  provided 
for  rapping  both  the  discharge  and  the  collecting  electrodes  in  order  to 
remove  from  time  to  time  any  dust  which  may  have  adhered  to  them. 
The  levers  for  operating  the  pipe  rappers  may  be  clearly  seen  in  the 
photograph.  The  bottom  header  is  a  reinforced  concrete  chamber  into 
which  the  collecting  electrode  pipes  project  and  in  which  the  collected 
material  is  deposited.  This  is  later  removed  by  hand  through  doors 
which  are  provided  for  this  purpose.  Should  it  be  desirable  similar 
installations  could  be  readily  provided  with  hoppers  and  screw  conveyors 


FIG.  15. 

so  that  the  collected  dust  could  be  taken  out  of  the  precipitator  con- 
tinuously and  automatically.  This  precipitator  occupies  a  space  ap- 
proximately 17  ft.  wide  by  28  ft.  long  and  has  an  overall  height  of 
about  35  ft.  The  amount  of  power  required  to  operate  the  installation 
is  about  18  KW. 

Figure  15  is  a  drawing  giving  the  general  arrangement  and  overall 
dimensions  of  a  precipitator  of  the  horizontal  flow  or  plate  type,  designed 
and  installed  by  the  Research  Corporation,  and  Fig.  13  is  a  view  looking 
in  a  lengthwise  direction  through  a  precipitator  of  this  kind  which  was 
installed  in  a  chamber  acid  plant  near  Baltimore,  Maryland,  and  which 
is  particularly  designed  to  withstand  the  high  temperatures  at  which 
the  gases  must  be  cleaned  in  such  a  plant.  This  installation  operates 
at  a  gas  temperature  of  1,100°F.,  while  occasionally  temperatures  as 
high  as  1,400°F.  have  been  recorded  in  the  precipitator. 

A  precipitator  of  the  size  shown  in  Fig.  14  will  clean  the  hot  gases 
produced  by  the  roasting  of  40  to  45  tons  of  fines  pyrites  per  twenty- 


90  AMERICAN  SULPHURIC  ACID  PRACTICE 

four  hours.  With  a  sulphur  dioxide  concentration  of  7K  per  cent  to 
8  per  cent  this  means  that  the  volume  of  gas  passing  through  the  in- 
stallation is  about  17,500  cu.  ft.  per  minute  at  a  temperature  of  1,100°F. 

As  will  be  noted  from  an  inspection  of  Fig.  15,  the  precipitator  is 
divided  into  two  sections,  each  of  which  is  provided  with  a  damper  at 
both  inlet  and  outlet  ends.  This  makes  it  possible  to  shut  off  either 
section  from  the  system  when  inspection  or  repair  is  required  or  when 
it  is  desired  to  clean  the  electrodes.  Such  cleaning  may  be  necessary 
every  few  days  if  a  very  dusty  ore  is  being  roasted  in  the  furnaces. 
For  the  above  reason  it  is  desirable  to  so  design  the  plant  that  each  sec- 
tion will  have  sufficient  capacity  to  handle  all  the  gas  for  short  periods 
of  time  and  in  this  way  continuity  of  operation  with  clean  gas  is  prac- 
tically assured. 

Among  the  more  important  benefits  obtained  by  the  use  of  the  Cot- 
trell  Processes  for  cleaning  roaster  gases  in  sulphuric  acid  manufacturing 
plants  the  following  may  be  mentioned: ' 

1.  The  quality  of  the  acid  is  improved,  due  to  the  removal  of  the 
dust  carried  by  the  furnace  gases. 

2.  More  efficient  operation  of  the  nitrating  pots  can  be  obtained  due 
to  the  absence  of  dust  in  the  gas  at  this  point  in  the  system. 

3.  Plant  shutdowns  for  cleaning  the  Glover  towers,  with  the  atten- 
dant loss  of  acid  and  limitation  of  production,  are  avoided. 

4.  The  life  of  the  lead  chambers  is  increased,  due  in  part  to  elimination 
of  dust  deposition. 

5.  A  material  is  collected  usually  having  more  than  sufficient  value 
to  carry  the  operating  cost  of  the  installation. 

The  simplest  dust  settler  is  an  enlargement  of  the  gas  flue  to 
reduce  the  gas  velocity.  A  considerable  amount  of  valuable  data 
has  been  gathered  on  this  method  of  dust  settling,  and  it  is  pos- 
sible to  design  a  dust  chamber  of  this  kind  with  assurance  as  to 
its  performance. 

It  seems  to  be  well  established  that  reduction  of  the  velocity 
of  the  gas  stream  to  not  over  5  ft.  per  second  is  necessary  to 
allow  proper  settling  within  a  reasonable  distance  of  travel. 
Even  at  this  rate  of  speed  a  flue  of  moderate  height,  say  10  ft., 
will  have  to  be  50  ft.  or  more  long  to  allow  the  dust  particles  to 
settle  out.  It  will  be  readily  seen  that  for  a  large  acid  unit  a 
dust  chamber  of  this  type  requires  a  great  deal  of  ground  space. 

Baffle  walls  to  make  the  gas  take  a  tortuous  course  are,  in 
this  form  of  dust  chamber,  of  doubtful  value.  One  baffle 
immediately  in  front  of  the  inlet  opening  is  good  to  spread  the 
gas  stream,  but  if  a  large  number  of  baffles  are  put  in  they  impede 


DUST  SETTLING  APPARATUS 


91 


the  draft,  raise  the  gas  velocity,  and  often  give  poorer  net  results 
than  empty  chambers. 

Wires  or  chains  hung  in  a  dust  chamber  of  this  type  have  a 
very  good  effect.  Their  virtue  of  course  lies  in  the  fact  that  dust 
particles  impinge  on  them  and  lose  their  velocity  and  fall  or  else 
cling  to  the  wires  or  chains.  They  do  not  interfere  with  draft  to 
any  serious  extent.  It  is  well  to  provide  some  means  of  shaking 
suspended  wires  or  chains  as  dust  clings  to  them  to  some  extent. 

An  interesting  account  of  the  performance  of  dust  chambers 
hung  with  wires  at  the  Copper  Queen  smeltery  is  given  in  an 
article  by  Geo.  B.  Lee  in  the  Engineering  and  Mining  Journal  of 
September  10,  1910.  Two  tests  described  showed  that  in  a 
100  ft.  long  chamber  with  gas  velocity  about  4^  ft.  per  sec., 


Dusi- Drawn  through 
Holes  in 


1 


^ 


Section  A-A    Section  A-A 
Howard  Chamber  Wxige  Chamber 


FIG.  16. 


62.8  per  cent  of  the  total  dust  was  deposited  with  the  chamber 
empty,  and  77  per  cent  when  hung  with  wires. 

Several  interesting  proposals  have  been  made  along  the  lines 
of  inserting  shelves  into  the  chambers,  the  idea  being  that  by 
using  them  the  distance  which  a  dust  particle  must  fall  before  it 
finds  a  resting  place  is  greatly  reduced.  The  Howard  dust 
chamber  which  provides  horizontal  metal  shelves  a  few  inches 
apart  is  one  example  of  this.  The  Wedge  dust  chamber  does  the 
same  thing  except  that  the  shelves  slope  sharply  toward  the 
outside  walls  and  in  that  way  the  dust  all  slides  down  against  the 
walls  and  can  be  more  easily  drawn.  This  principle  is  a  good  one 
so  far  as  settling  dust  is  concerned,  but  the  structural  difficulties 
are  considerable  for  large  units  or  where  the  gases  are  very  hot. 

Figure  16  shows  a  longitudinal  section  which  applies  to  either 
the  Howard  or  the  Wedge  chambers  described,  while  the  trans- 
verse sections  show  the  horizontal  position  of  the  Howard 
shelves  and  the  inclined  position  of  the  Wedge  shelves.  The 
Howard  chamber  has  been  installed  in  several  plants  with 


92 


AMERICAN  SULPHURIC  ACID  PRACTICE 


satisfactory  results.     I   do  not   know   whether  any  chambers 
following  the  Wedge  plan  have  been  built. 

Dust  chambers  employing  the  centrifugal  principle  have  been 
used  in  some  places  for  acid  work.  They  have  not  been  as 
popular  as  their  merits  warrant.  A.  P.  O'Brien  many  years 
ago  used  such  a  dust  chamber  at  Richmond,  Va.  This  is  de- 
scribed in  the  Mineral  Industry,  Volume  9,  as  retaining  75  per 
cent  of  the  dust  entering,  which  is  very  good.  More  modern 
applications  of  this  plan  have  been  made  at  the  American  Steel 
and  Wire  Company's  acid  plants  at  Donora,  Pa.,  in  connection 
with  Hegler  roasters,  and  at  the  Garfield  Chemical  and  Manu- 
facturing Company's  plant  at  Garfield,  Utah,  where  fine  copper 
concentrate  is  roasted  in  Herreshoff  furnaces. 


Plan 


FIG.  17. 


Chambers  of  this  type  are  cylindrical  with  gas  inlet  tangential 
and  near  the  top,  and  with  gas  outlet  through  a  central  pipe  lead- 
ing from  a  point  near  the  bottom.  Figure  17  shows  the  essential 
features.  The  velocity  of  the  entering  gas  should  be  as  high  as 
possible  without  too  much  impeding  the  draught.  Good  clearance 
requires  entering  gas  velocity  not  under  25  t.  per  second. 

Centrifugal  dust  chambers  are  very  small  and  compact  for  the 
work  they  accomplish  and  have  much  to  recommend  them  for 
acid  plants  for  that  reason.  In  cases  where  it  is  desirable  to 
hold  up  the  temperature  of  the  furnace  gases  so  that  the  Glover 
tower  will  concentrate  well,  the  small  radiating  surface  of  the 
centrifugal  chamber  is  an  advantage. 

The  Anaconda  Copper  Mining  Co.  has  in  its  acid  plants 
two  dust  chambers  of  a  unique  design  which  has  probably  not 
been  used  elsewhere.  These  chambers  have  given  excellent 
results  and  are  so  compact  that  they  deserve  description.  They 


DUST  SETTLING  APPARATUS 


93 


use  both  the  principles  of  decreased  velocity  and  change  of 
direction  to  accomplish  clearance.  The  form  of  this  chamber  is 
a  cylinder  with  inverted  conical  bottom,  and  in  general  appearance 
resembles  the  centrifugal  chambers. 

Referring  to  Fig.  18,  the  gas  enters  through  flues  1-1  into 
space  2,  distributes  radially,  passes  through  the  4-in.  vertical 
slots,  and  rises  into  space  3.  Space  2  is  separated  from  space  3 
by  reinforced  concrete  cone  5-5.  From  space  3  the  gas  leaves 
the  chamber  through  passage  4  which  does  not  communicate 


Walls,  with  Vertical 
Slots. 4  "Wide  , 


Section  A -A 


Section  B-B 


FIG.  18. 


with  space  2.  The  dust  which  drops  in  space  3  falls  through  the 
vertical  cast  iron  pipe  6  and  is  drawn  off  with  the  dust  which  falls 
in  space  2,  at  gate  7.  This  chamber  is  entirely  self  cleaning. 

The  original  chamber  at  Anaconda  cleans  the  gases  from 
roasting  150  tons  of  copper  concentrate  per  24  hours,  all  of  which 
passes  j^-in.  screens.  It  is  32  ft.  in  diameter  and  43  ft.  high 
outside.  It  offers  very  little  resistance  to  the  passage  of  the 
gas  and  in  this  respect  is  better  than  the  centrifugal  chambers. 
Its  cost  of  construction  is  somewhat  higher  than  that  of  a  centrifu- 
gal chamber,  but  it  is  a  very  satisfactory  apparatus  from  an 
operating  point  of  view. 


CHAPTER  VIII 
THE  GLOVER  TOWER 

The  Glover  tower  is  the  first  division  of  the  acid  plant  proper. 
It  receives  through  a  flue  entering  it  near  its  bottom  the  gas 
from  the  burners.  This  gas  contains  essentially  S02,  oxygen, 
nitrogen  and — if  nitre  is  potted  in  the  flu& — a  small  amount  of 
NO.  Its  temperature  may  be  up  to  1,000°F.  or  1,200°F.  Into 
the  top  of  the  Glover  tower  are  fed  nitrous  vitriol  (60°  sulphuric 
containing  N2O3  in  solution),  and  chamber  acid  about  50°Be. 
The  purpose  of  the  tower  is  to  produce  an  intimate  contact 
between  the  gas  and  the  acid. 

With  this  statement  of  the  duties  of  the  Glover  tower  in 
view,  it  is  clear  that  the  tower  must  be  constructed  in  such  a  way 
as  to  be  acid  and  gas  tight  against  pressures  of  a  few  ounces, 
and  it  must  be  of  such  materials  and  built  in  such  a  way  as  to 
withstand  the  action  of  gas  at  1,000°F.  and  sulphuric  acid  of 
60°  or  610Be".  at  300°F. 

A  modern  Glover  Tower  consists  of  a  lead  shell  supported 
by  steel  or  wood  framework,  a  lining  of  acid-  and  heat-resisting 
brick,  and  a  packing  of  acid-  and  heat-resisting  material  placed 
in  such  a  way  that  gas  may  ascend  through  it  freely  and  acid 
descend  over  its  surfaces.  The  structure  is  built  in  a  lead, 
brick-lined  pan  which  may  be  integral  with  the  tower  or  fairly 
distinct  from  it.  A  brick-lined  flue  enters  near  the  bottom  to 
deliver  the  hot  furnace  gases  into  the  tower,  and  another  flue  of 
bare  lead  leaves  the  top  of  the  tower  and  carries  the  gases  to  the 
chambers. 

As  it  is  desirable  that  the  acid  which  issues  from  the  Glover 
tower  shall  flow  by  gravity  to  coolers  and  tanks,  the  tower 
proper  is  built  on  a  suitable  foundation  from  10  to  20  ft.  high. 

The  weight  of  the  tower  is  very  great  and  the  stability  of  the 
foundation  must  be  beyond  question.  In  modern  plants  rein- 
forced concrete,  or  structural  steel  on  a  heavy  concrete  base  or 
piers,  are  the  forms  of  construction  used.  A  smooth  level  floor 
at  the  desired  height  is  obtained  by  one  of  these  methods,  and 
on  it  is  laid  down  a  sheet  of  light  lead — 6  or  8  Ib.  per  square  foot 

94 


THE  GLOVER  TOWER  95 

— as  a  protection  against  leakage  or  overflow  of  acid.  This  lead 
extends  out  beyond  the  edge  of  the  foundation  a  few  inches,  or 
is  turned  up  to  form  a  shallow  pan  which  is  drained  by  pipes. 

The  pan  of  the  Glover  tower  is  frequently  made  of  lead  weigh- 
ing 60  Ib.  per  square  foot  i.e.,  about  1  in.  thick.  It  may  be 
made  somewhat  lighter  with  safety  if  the  masonry  lining  is  well 
done. 

The  sides  and  top  of  the  Glover  tower  are  of  lead  not  less  than 
10  Ib.  per  square  foot  and  better  15  or  20  Ib. 

A  sturdy  framework  of  wood  or  steel  or  a  combination  of  the 
two,  supports  the  lead,  and,  above  the  top  of  the  tower,  a  plat- 
form carrying  acid  tanks.  This  frame  consists  usually  of  4 
posts  or  columns  with  horizontal  members  between  them  which 

-Woect  Joists  "*|| 

Lead  Straps  {turned 0n±  LjJ         Tower 


lead  Covered  Iren  Pi'p<?& 
- Lead  Loops      J^^     Twer  Tcp^ 


JL' 

lron  x^y 
Hook  1 


'•-Angle  Irons 
iron  ,*a  turned  over-  . 


FIG.  19. 

support  the  lead,  or  which  carry  small  vertical  pieces  which 
support  the  lead.  Horizontal  or  vertical  straps  are  burned  to  the 
lead  sheets  and  nailed  or  bolted  to  the  supporting  members  of 
the  framework.  As  the  lead  sheets  are  supported  inside  by  close 
contact  with  the  lining  wall,  the  outside  straps  on  the  side  sheets 
need  not  be  very  close  together. 

The  top  lead  is  supported  by  straps  nailed  to  wooden  joists 
or  by  loops  of  lead  passing  over  iron  pipes,  or  by  small  iron  hooks 
supporting  rods  burned  to  the  lead.  Several  of  these  schemes 
are  shown  in  Fig.  19. 

As  mentioned  earlier  the  pan  of  the  Glover  tower  is  often 
quite  distinct  from  the  tower  proper  which  sits  in  it,  though 
sometimes  the  upper  edge  of  the  pan  and  the  lower  edge  of  the 
side  sheets  are  burned  together,  in  which  case  the  pan  is  not  very 


96  AMERICAN  SULPHURIC  ACID  PRACTICE 

clearly  defined.  It  cannot  be  said  that  either  plan  is  very  dis- 
tinctly better  than  the  other  though  it  is  easy  to  get  into  trouble 
with  the  latter  method  if  the  details  are  not  carefully  designed. 
The  pan  and  the  sides  of  the  Glover  tower  are  lined  with  brick, 
usually  in  recent  years  laid  up  in  acid  proof  mortar,  though 
formerly  and  sometimes  now,  laid  dry.  So  much  stress  has  been 
put  upon  the  quality  of  the  brick  used  for  this  purpose  that  it 
seems  to  be  a  rather  common  idea  that  very  exceptional  clays, 
and  methods  of  manufacture  are  necessary.  It  is  difficult  to 
lay  down  any  analysis  figures  which  show  the  fitness  of  brick 
for  this  purpose.  Of  course  the  higher  the  sum  of  silica  and 
alumina  the  better.  The  sum  of  CaO  and  MgO  should  not  be 
over  3  or  4  per  cent.  Very  satisfactory  acid  resisting  brick  may 
contain  up  to  6  or  7  per  cent  FeO.  As  a  matter  of  fact  in  almost 
any  part  of  the  United  States  one  can  find  within  two  or  three 
hundred  miles  entirely  satisfactory  brick  for  making  tower  linings. 
As  a  test  if  the  brick  is  mechanically  sound  and  strong,  it  should 
be  soaked  for  a  week  or  more  in  sulphuric  acid  and  then  allowed 
to  stand  in  the  weather  for  several  weeks  or  as  long  as  one  can 
wait.  If  no  spalling  or  cracking  or  swelling  occurs  after  a  long 
period  of  weathering,  the  brick  will  stand  up  well  in  the  tower. 

The  mortar  used  in  laying  the  brick  consists  of  silicate  of  soda 
and  finely  ground  silica  with  a  small  percentage  of  barium  sul- 
phate if  desired.  This  mortar  sets  up  very  slowly  as  the  set  is 
due  to  evaporation  of  water  only.  After  this  initial  set  has  taken 
place,  sulphuric  acid  is  run  over  the  brickwork.  This  reacts 
with  the  silicate  of  soda  and  gives  the  mortar  a  permanent  set. 
The  bottom  of  the  pan  is  lined  with  4  or  6  in.  of  brick.  If  the 
pan  is  open,  the  sides  are  lined  with  4  in.  of  brick.  The  lining 
wall  of  the  tower  proper  is  18  to  24  in.  thick  in  the  lower  part 
where  the  heat  is  high.  A  few  feet  above  the  top  of  the  gas  inlet 
flue  the  thickness  can  be  decreased  and  after  the  middle  of  the 
tower  is  reached  9  to  12  in.  thickness  is  correct. 

Figure  20  shows  the  lining  and  packing  of  a  Glover  tower.  The 
packing  of  Glover  towers  is  essentially  acid-resisting  solid  mate- 
rial which  shall  present  a  large  amount  of  surface  to  the  gas 
and  acid  passing  through  it,  thereby  causing  intimate  and  thor- 
ough contact  between  them.  Many  materials  have  been  used 
for  packing.  Coke  was  formerly  well  thought  of  because  it 
offered  much  surface  and  was  light.  It  is  rarely  used  now  be- 
cause it  is  not  so  permanent  or  satisfactory  as  other  things.  In 


>WER 


97 


the  course  of  months  or  a  fe  •  breaks  up  and  impedes 

the  passage  of  the  gas  and  ha,-  ml**  u  ,ved — an  expensive  and 
dangerous  job.  Like  any  other  noii  -,-u  Anmetrical  packing,  coke 
exerts  some  lateral  pressure  on  the  walls  of  the  tower,  which  is 
undesirable. 


'id  f&  Cooler 


FIG.  20. 


Another  class  of  material  used  formerly  but  not  much  now,  is 
rough  fragments  of  quartz  or  other  natural  or  artificial  silicious 
material.  This  is  better  than  coke  in  that  it  does  not  break  down 
readily,  but  it  is  open  to  the  objection  of  creating  lateral  thrust. 
In  using  these  rough  unsymmetrical  packings  one  cannot  fore- 
tell very  accurately  what  resistance  to  gas  passage  will  be 
encountered,  and  sometimes  very  unexpected  things  in  this  way 
are  encountered. 
7 


98  AMERICAN  SULPHURIC  ACID  PRACTICE 

Much  the  most  satisfactory  kind  of  packing  is  acid-resisting 
brick  or  shaped  pieces  of  symmetrical  form,  laid  up  so  that  all 
the  thrust  is  downward  and  none  on  the  walls.  With  such 
packing  one  can  accurately  determine  how  much  area  for  gas 
passage  exists  and  how  much  wetted  surface  for  gas  acid  contact. 
In  using  unsymmetrical  packing  these  things  are  very  indefinite. 
With  symmetrical  packings  also  there  is  no  thrust  on  the  walls 
of  the  tower. 

There  are  many  kinds  of  symmetrical  packings,  some  patented 
and  some  for  which  very  exclusively  superior  virtues  are  claimed. 
In  deciding  between  the  various  kinds  available  one  should  con- 
sider that  the  most  elaborately  designed  shapes  do  not  as  a  matter 
of  hard  practical  fact  give  much  better  results  than  plain  rec- 
tangular brick  of  standard  dimensions.  If  packing  is  to  be  used 
at  a  point  near  to  the  factories  which  make  the  special  shapes  it 
is  well  enough  to  take  advantage  of  the  fact  and  use  them.  It 
does  not  pay  however  to  ship  fancy  packings  many  hundreds  of 
miles  if  good  standard  brick  can  be  obtained  locally. 

Above  the  top  of  the  Glover  tower  are  located  two  tanks, 
one  to  receive  nitrous  vitriol  and  the  other  chamber  acid.  These 
acids  are  fed  into  the  tower  through  suitable  distributors  which 
should  uniformly  spread  the  acids  over  the  entire  top  surface 
of  the  packing.  The  nitrous  vitriol  and  chamber  acid  are  best 
kept  separate  until  they  are  inside  the  tower,  because  on  mixing 
them  some  fuming  off  of  the  nitrogen  oxids  occurs. 

The  chief  function  of  the  Glover  tower  is  to  denitrate  the 
nitrous  vitriol,  the  solution  of  N203  in  sulphuric  acid,  which 
comes  from  the  Gay  Lussac  towers.  This  nitrous  vitriol  is 
broken  up  by  the  hot  SO2,  the  acid  is  freed  from  its  nitrogen 
compounds,  which  are  mostly  reduced  to  the  form  NO,  a  gas, 
which  proceeds  with  the  gas  stream  into  the  chambers. 

In  order  that  this  action  may  be  complete  and  the  acid  issuing 
from  the  Glover  tower  be  entirely  free  from  nitrogen-oxides  it 
is  necessary  that  the  nitrous  vitriol  be  diluted  with  water  or  weak 
acid  at  the  top  of  the  tower.  It  is  necessary  however  that  the 
acid  issuing  from  the  tower  be  not  less  than  59°Be.  as  that  is 
what  the  Gay  Lussacs  require.  This  requirement  limits  the 
amount  of  weak  acid  which  may  be  introduced.  Fortunately 
the  usual  roaster  or  burner  gas  has  a  sufficiently  high  tempera- 
ture to  allow  the  introduction  of  much  more  weak  acid  that  the 
amount  necessary  to  accomplish  complete  denitration,  and  the 


THE  GLOVER  TOWER  99 

Glover  tower  becomes  a  means  of  concentrating  almost  all  of 
the  chamber  acid  to  59°  or  60°  acid.  This  is  its  second  function. 

A  third  function  though  an  incidental  one  is  that  the  roaster 
gas  is  cooled  to  a  temperature  at  which  it  will  not  harm  bare 
lead. 

Of  course  the  concentrating  capacity  of  a  Glover  tower  depends 
largely  upon  the  temperature  of  the  roaster  gases.  If  they  enter 
the  tower  at  1,000°F.  all  the  chamber  acid  can  be  concentrated 
to  60°  or  even  61°.  If  their  temperature  be  two  or  three  hundred 
degrees  lower  not  all  the  chamber  acid  can  be  concentrated. 

In  the  matter  of  dimensions  and  of  cubic  contents  there  seems 
to  be  a  surprising  difference  of  opinion,  shown  by  modern 
designers.  Varying  S02  percentages  and  temperatures  account 
for  some  of  the  difference  but  by  no  means  all. 

Lunge  states  that  the  net  packed  volume  of  a  Glover  tower 
should  be  in  the  neighborhood  of  320  cu.  ft.  per  ton  of  sulphur 
or  about  80  cu.  ft.  per  ton  of  60°  acid  made.  This  refers  to 
European  practice  and  small  units. 

A  large  American  plant  recently  erected  has  a  Glover  tower 
whose  net  packed  volume  amounts  to  33  cu.  ft.  per  ton  of  60° 
acid. 

Many  American  plants  erected  within  the  last  few  years  have 
around  50  cu.  ft.  per  ton  of  60°  acid  produced,  and  that  figure 
probably  approaches  modern  opinion  of  this  point. 

The  vertical  dimension  of  the  packing  is  usually  from  20  to  30 
ft.  There  is  some  possibility  of  making  this  dimension  too  great 
to  be  good  for  the  concentrating  capacity  of  a  tower  in  that  the 
gas  temperature  may  fall  so  low  that  condensation  will  take  place. 
If  gases  entering  the  tower  are  hot,  say  over  1,000°F.,  a  30  ft. 
dimension  is  quite  proper,  but  if  the  gas  temperature  is  below 
800°  it  is  well  to  hold  the  vertical  dimension  of  the  packing  lower. 

The  horizontal  area  of  the  packing  will  of  course  be  fixed  by 
the  cubic  contents  and  the  height,  and  will,  from  the  above,  vary 
between  1.66  and  2.5  sq.  ft.  per  ton  60°  acid  produced.  The 
overall  height  of  the  Glover  tower  is  usually  from  10  to  15  ft. 
more  than  the  height  of  the  packing  proper  to  allow  for  the  gas 
distribution  chamber  below  and  the  acid  distribution  space  above 
the  packing. 

The  outside  horizontal  dimensions  are  greater  than  the  hori- 
zontal dimensions  of  the  packing  by  3  or  4  ft.  to  allow  for  the 
lining  walls. 


100  AMERICAN  SULPHURIC  ACID  PRACTICE 

As  an  example  of  the  above  observations  a  Glover  tower  for 
a  unit  to  produce  100  tons  of  60°  acid  per  day  would  assume 
dimensions  as  follows: 

Cubic  contents  of  packing  @  50  cu.  ft.  per  ton  60°  acid  5,000  cu.  ft. 
Vertical  dimension  of  packing  25  ft. 
Area  of  packing  5,OQO  4-  25  =  200  sq.  ft. 

Assume  that  the  tower  has  square  section,  than  the  horizontal 
dimensions  of  the  paking  will  be  14  ft.  2  in. 

The  overall  height  of  the  tower  will  be  25  +  15  =  40  ft. 

The  outside  horizontal  dimensions  will  be  about  17  ft.  X  17  ft. 


CHAPTER   IX 
THE  CHAMBERS 

The  gas  mixture  coming  from  the  Glover  tower  consists  of 
S02,  NO,  0,  N,  and  water  and  weak  acid  vapor.  A  period  of 
from  1  to  2  hours  is  required  for  reaction  between  them  sufficient 
to  convert  substantially  all  of  the  SO2  into  sulphuric  acid. 

A  place  in  which  the  gases  may  react,  a  chamber  or  series  of 
chambers  then,  will  be  required  of  such  volume  that  each  portion 
of  gas  mixture  will  occupy  from  1  to  2  hours  in  its  passage  from 
entrance  to  exit  of  the  series.  Liquid  sulphuric  acid  forms  and 
condenses  within  the  chambers,  which  must  therefore  be  con- 
structed of  such  material  and  in  such  fashion  as  to  retain  liquid 
sulphuric  acid. 

The  acid-forming  reactions  are,  taken  collectively,  exothermic. 
It  is  essential  for  the  proper  progress  of  the  reactions  that  the 
temperature  of  the  gas  mixture  shall  not  rise  much  above  the 
boiling  point  of  water.  It  is  therefore  necessary  that  the  cham- 
bers be  constructed  of  such  material  and  in  such  fashion  that  the 
heat  of  reaction  can  be  readily  carried  away  by  radiation. 

These  considerations  together  with  the  experience  of  many 
years  dictate  the  volume,  the  materials,  and  the  method  of 
construction  of  the  chambers. 

Sheet  lead  possesses  a  desirable  combination  of  the  essential 
characteristics  so  predominantly  that  it  is  universally  used  as  the 
basic  material  for  chamber  construction.  It  is  cheap,  it  resists 
acid  well,  it  can  be  readily  shaped,  and  its  pieces  can  be  burned 
together  to  make  gas-  and  acid-tight  joints.  Furthermore  it 
conducts  heat  well.  Other  materials  have  been  tried  from  time 
to  time  but  none  so  well  meets  the  requirements. 

It  has  been  found  best  to  provide  instead  of  one  single  large 
chamber  several  smaller  ones,  usually  three  or  more.  Several 
good  reasons  for  this  exist.  Mixing  and  stirring  up  the  gas  mix- 
ture accomplished  by  passing  through  flues  from  one  chamber  to 
another  has  been  found  to  accelerate  the  reactions.  By  dividing 
the  space  into  several  small  chambers  more  radiating  surface  is 

101 


102*         AMERICAN  SULPHURIC  ACID  PRACTICE 

provided  than  if  a  single  chamber  were  used.  It  is  more  con- 
venient structurally  to  build  several  small  chambers  than  one 
large  one.  A  modern-  chamber  set  therefore  consists  of  from 
three  to  ten  chambers  in  series. 

The  individual  chamber  consists  of  three  parts,  pan,  side  or 
"curtain"  walls,  and  top,  all  of  sheet  lead.  The  pan  is  ordi- 
narily of  lead  weighing  8  or  10  Ib.  per  square  foot — i.e.  ^  to  %Q 
in.  thick — with  the  bottom  horizontal  and  the  sides  from  18  to  30 
in.  high.  The  pan  is  designed  to  be  a  reservoir  for  the  acid  made 
in  the  chamber  and  is  supported  strongly  so  that  it  will  safely 
carry  acid  to  within  an  inch  or  two  of  its  top  edge. 

The  side  or  curtain  walls  extend  from  the  upper  edge  of  the  pan 
to  the  top  of  the  chamber.  They  are  of  sheet  lead  of  6  to  10 
Ibs.  per  sq.  ft.  in  weight.  They  are  supported  by  lead  straps 
burned  to  the  sheets  and  fastened  to  a  wood  or  steel  framework 
surrounding  the  chamber.  It  was  formerly  common  to  allow 
the  bottoms  of  the  curtain  sheets  to  extend  down  into  the  pan 
to  within  about  2  in.  of  the  bottom.  The  acid  in  the  pan  then, 
so  long  as  it  was  maintained  more  than  2  in.  in  depth,  made  a  seal 
which  retained  the  gas.  This  plan  though  followed  for  years  and 
still  used  sometimes  is  not  a  sensible  one.  It  wastes  lead  on 
original  construction  and  after  about  two  years  that  part  of  the 
lead  which  is  immersed  in  the  acid  becomes  so  corroded  that  holes 
appear  and  much  repair  work  or  even  reskirting  becomes  neces- 
sary. The  usual  plan  of  recent  years  is  to  burn  together  the  top 
edge  of  the  pan  and  the  bottom  edge  of  the  curtain  walls.  Figure 
21  shows  the  two  methods. 

The  top  of  the  chamber  is  usually  of  lead  of  the  same  weight  as 
the  curtain  walls.  It  is  ordinarily  horizontal  and  the  sheets  are 
supported  by  frequent  straps  fastened  to  rafters  of  wood  or 
steel.  The  sheets  of  the  top  and  the  curtain  walls  are  burned 
together  when  they  meet. 

The  bottoms  of  the  chambers  should  always  be  far  enough 
above  ground  to  allow  convenient  inspection  for  leakage,  say  6 
or  7  ft.  minimum,  so  that  a  man  may  walk  about.  This  is  im- 
portant because  leaks  invariably  develop  and  if  the  chamber  pans 
were  laid  on  the  ground  much  loss  of  acid  and  damage  to  founda- 
tions and  pans  would  result  before  the  trouble  was  detected. 

Concrete  piers  properly  placed  in  the  ground  to  carry  the 
weight  of  the  chamber  structure  and  the  pan  full  of  acid  are  first 
set.  On  these  are  fixed  wood  or  steel  posts  surmounted  by  wood 


THE  CHAMBERS 


103 


or  steel  sills.  On  the  sills  is  laid  down  a  wood  floor  to  carry  the 
chamber  pans.  Between  arid  around  the  pans  the  floor  is  of  wood 
slats  well  apart,  or  perforated  steel,  a  construction  in  any  event 
which  will  allow  free  circulation  of  air  up  the  sides  of  the  cham- 
bers. It  is  well  to  build  the  floor  on  which  the  pans  are  to  rest 
of  plain  boards,  not  matched — tongue  and  grooved — in  order  that 
leaks  may  be  readily  located.  If  the  floor  is  too  tight  it  may  be 
difficult  to  decide  just  where  the  hole  in  the  lead  is,  as  the  acid 
may  travel  some  distance  before  it  finds  a  crack  or  crevice  through 
which  it  can  issue. 

The  lead  walls  and  tops  of  the  chambers  are  supported  by 
wood  or  steel  framework  or  a  combination  of  the  two.  For  very 
large  chambers  steel  is  necessary  because  of  the  long  spans  and 
great  height  of  columns.  For  small  chambers  wood  is  more 


Acid 


FIG.  21. 

economical  and  perhaps  better  adapts  itself  to  fastening  to  the 
lead.  Certainly  it  is  not  so  fireproof  though  there  is  not  any 
unusual  fire  hazard  about  chambers  inherent  in  the  process 
itself. 

Two  somewhat  different  general  plans  of  wood  framing  for 
supporting  the  curtain  walls  have  been  used.  The  first,  which  is 
probably  most  used,  provides  posts  of  rather  large  section  spaced 
perhaps  6  or  8  ft.  apart.  Secured  to  these  are  lighter  horizontal 
rails  3  or  4  ft.  apart  vertically.  Horizontal  lead  straps  to  corre- 
spond to  these  rails  are  burned  to  the  lead  curtain  walls  and  nailed 
or  cleated  to  the  rails.  On  the  top  of  the  posts  rests  a  heavy  cap 
or  crown  timber.  The  curtain  sheets  are  turned  back  over  the 
top  of  this  crown  piece  and  part  way  down  its  outside  and  there 
nailed.  The  theory  of  this  method  of  support  is  that  almost  all 
of  the  weight  of  the  curtain  sheets  is  carried  by  the  crown  piece, 
and  the  straps  on  the  sides  simply  prevent  lateral  movement. 


104 


AMERICAN  SULPHURIC  ACID  PRACTICE 


There  are  of  course  many  variations  of  detail  in  this  scheme. 
Figure  22  shows  the  essential  features. 

The  other  system,  shown  in  Fig.  23  provides  vertical  posts  or 
studs  of  comparatively  small  cross  section,  much  closer  together, 


fl 


FIQ.  22. 


say  20  to  30  in.  No  horizontal  rails  are  used.  The  straps  are 
burned  to  the  curtain  walls  vertically,  a  row  to  correspond  to 
each  vertical  stud,  and  cleated  to  the  studs.  A  light  cap  at  the 
top  of  the  studs  serves  merely  to  hold  them  in  position.  The 


HJ     HJ 


FIG.  23. 


curtain  sheets  are  not  turned  over  it  but  are  curved  in  toward 
the  center  line  of  the  chamber.  The  studs  are  appropriately 
braced  and  held  in  position  by  horizontal  and  diagonal  members 
spiked  to  their  outside  faces.  When  the  sides  of  the  chamber  pan 


THE  CHAMBERS  105 

are  of  10  Ib.  lead  and  the  studs  are  not  more  than  24  in.  apart 
it  is  not  necessary  to  support  the  pan  sides  with  planks.  The 
theory  of  support  by  this  method  is  that  each  vertical  strap 
supports  its  particular  small  section — perhaps  four  square 
feet — of  the  curtain  sheet,  and  the  whole  load  is  uniformly 
distributed. 

There  is  some  difference  of  opinion  as  to  which  is  the  better  of 
these  two  general  systems  of  support.  The  first  described  plan 
has  been  more  generally  used,  but  the  second  plan  has  some  very 
important  advantages  in  practice  as  well  as  in  theory.  Lead  is 
a  metal  which  has  practically  no  elasticity.  Under  stress,  par- 
ticularly when  warm,  it  flows.  When  a  sheet  20  or  30  ft.  long  is 
suspended  from  a  crown  piece  as  described,  with  light  horizontal 
straps  at  rather  large  intervals  to  prevent  sway,  it  unfortunately 
does  not  all  remain  just  where  it  was  placed.  When  the  chamber 
is  heated  up  to  200°F.  a  considerable  expansion  occurs.  When  a 
stop  and  cooling  takes  place,  it  does  not  go  back  up  again.  On 
again  heating,  downward  expansion  again  takes  place.  Further- 
more there  is  some  creep  caused  by  stretching  or  flow.  The  net 
result  of  these  influences  in  the  course  of  a  year  or  two,  is  that 
much  of  the  load  is  transferred  to  the  straps  where  it  does  not 
belong,  and  distortion  of  the  curtain  sheets  results,  or  straps  are 
pulled  off,  usually  both.  Another  weak  feature  of  this  support 
plan  is  in  the  fact  that  behind  the  crown  piece  just  where  the 
strain  is  greatest  on  the  lead,  and  where  radiation  is  most  ob- 
structed, the  lead  is  inaccessible  for  repair. 

In  the  vertical-stud  system  each  small  rectangle  of  the  lead  is 
supported  by  its  strap  and  the  expansion  of  the  lead  with  heat- 
ing shows  itself  in  very  slight  curves  between  straps.  No  large 
unsightly  and  damaging  distortions  occur.  At  the  line  where  the 
side  turns  to  the  top,  the  lead  is  entirely  accessible.  From  an 
erection  point  of  view  this  framing  plan  is  excellent  also. 

Steel  framing  for  supporting  chamber  lead  has  been  increas- 
ingly used  of  late  years.  Its  use  has  been  necessary  in  some  of 
the  large  units  in  which  individual  chamber  dimensions  are  so 
great  as  to  make  timber  construction  out  of  the  question,  or  at 
least  very  awkward.  In  some  modern  plants  of  small  dimensions 
the  desire  for  permanency  and  fireproof  construction  has  dictated 
the  use  of  steel. 

The  construction  is  simple  and  usually  follows  the  idea  de- 
scribed first  above  under  wood  framing,  i.e.,  vertical  posts  or 


106  AMERICAN  SULPHURIC  ACID  PRACTICE 

columns  8  to  12  ft.  apart  are  used  with  horizontal  members  3 
or  4  ft.  apart  to  which  the  lead  is  attached  with  straps.  Angles 
are  probably  most  used  for  both  vertical  and  horizontal  members 
though  sometimes  I  beams  for  columns  and  channels  for  hori- 
zontal pieces  are  seen.  The  chamber  top  is  supported  by  I  beams 
or  pairs  of  channels  across  the  short  dimension  of  the  chamber, 
with  pairs  of  small  angles  between  them  running  longitudinally 
of  the  chamber  to  which  the  lead  straps  are  fastened. 

Chambers  should  always  be  protected  by  a  building.  The 
chief  reason  for  this  is  to  prevent  wind  pressure  from  reaching  the 
lead  Less  important  considerations  are  protection  from  sun, 
rain  and  snow,  and  facility  of  proper  control  of  the  process  in 
bad  weather.  The  chamber  framing  should  be  in  no  way  con- 
nected with  the  framing  or  walls  of  the  building  as  it  is  essential 
that  movement  of  the  building  due  to  wind  be  not  transmitted 
to  the  chambers.  Ample  openings  in  the  walls  below  the 
chamber  floor,  and  roomy  ventilators  in  the  roof  are  necessary  to 
assure  free  circulation  of  cool  air  along  the  side  walls  of  the  cham- 
bers. Modern  chamber  plants  are  housed  in  steel  or  brick 
buildings. 

It  has  been  mentioned  that  one  prime  object  of  dividing  the 
chamber  space  into  several  small  chambers  instead  of  using  a 
single  large  one  is  to  cause  mixing  and  invigorating  reaction  by 
passing  through  connecting  flues.  Much  thought  and  experi- 
mentation has  been  spent  upon  this  subject  of  connections  be- 
tween chambers. 

The  most  simple  plan  is  to  run  a  flue  from  the  centre  of  the  end 
of  one  chamber  to  the  centre  of  the  end  of  the  following  one. 
Another  similar  method  is  to  use  two  or  four  direct  horizontal 
flues  between  the  ends  of  the  adjoining  chamber.  Sometimes 
the  gas  is  taken  from  near  the  bottom  of  one  chamber  and  led  to 
a  point  in  or  near  the  top  of  the  following  one.  Or  a  flue  will 
leave  the  lower  left  hand  corner  of  the  end  of  a  chamber  and  enter 
the  upper  right  hand  corner  of  the  next  or  vice  versa,  the  object 
being  apparently  to  have  entrance  to  and  exit  from  a  given  cham- 
ber at  points  most  extremely  distant  from  each  other.  The 
purpose  of  all  these  latter  designs  is  to  avoid  having  dead  corners 
or  wedges  in  the  chambers  in  which  the  gas  moves  sluggishly 
or  not  at  all,  or  in  a  word  to  avoid  short  circuiting.  An  arrange- 
ment sometimes  used  which  is  intended  to  introduce  the  gas 
into  a  chamber  in  such  a  way  that  it  will  conform  to  the  natural 


THE  CHAMBERS 


107 


movement  of  the  reacting  gases  in  the  chamber  is  shown  in 
Fig.  24. 

This  is  based  on  the  idea  that  any  given  portion  of  gas  mixture 
will  proceed  through  the  chamber  in  a  spiral  course.  Radiation 
at  the  walls  causes  the  gas  nearby  to  cool  and  descend.  On 
reaching  the  bottom  it  is  forced  in  toward  the  centre  and  reaction 
heat  there  causes  it  to  rise  again  toward  the  top  where  it  is  drawn 
toward  the  side  again  by  the  descending  stream.  There  is 
meanwhile  a  forward  movement.  This  movement  of  course 
takes  place  on  each  side  of  the  central  vertical  plane.  Tlie  flue 
connections  shown  inject  the  gas  on  each  side  near  the  bottom 
and  direct  it  toward  the  centre  where  it  rises  and  immediately 
and  naturally  begins  its  double  spiral  progress. 


Elevation 


Plan 


FIG.  24. 


Many  designers  have  used  special  structures  between  the 
chambers  to  insure  thorough  mixing  of  the  gases  and  often 
cooling  as  well.  These  often  accomplish  the  work  for  which 
they  are  designed.  Sometimes  they  cost  more  money  than  an 
additional  plain  chamber  which  would  give  the  same  net  result 
in  tons  of  acid  made  and  the  intricacy  of  their  lead  work  some- 
times makes  for  heavy  repair  costs  after  they  are  a  few  years  old. 

In  the  1918  "Transactions  of  the  American  Institute  of  Chemical 
Engineers,"  Dr.  L.  A.  Thiele  describes  his  Multiple  Tangent 
System  of  introducing  gases  to  the  chambers. 

His  idea  is  to  avoid  the  large  amount  of  waste  space,  particu- 
larly in  the  corners,  where  the  circulation  in  the  chambers  is 
sluggish.  An  additional  advantage  is  a  very  considerable  saving 
in  area. 

Gas  is  introduced  from  the  top  of  the  Glover  tower,  through 
flues,  which  vary  in  area  and  length,  the  largest  in  area  being  the 
shortest;  this  makes  for  varying  rates  of  cooling,  thus  varying 
pressures  and  rates  of  flow-all  of  which  results  in  more  rapid  circu- 


108 


AMERICAN  SULPHURIC  ACID  PRACTICE 


lation  and  better  mixing.  The  flues  are  arranged  as  shown  in 
the  accompanying  sketch,  around  the  circumference  of  the  top, 
Fig.  25. 

If  the  outlet  should  be  in  the  centre  of  the  bottom,  the  gas 
would  be  a  spiral  cone,  the  outside  parts  of  the  bottom  being 
dead  space.  Thus  the  outlets  are  arranged  on  a  circle  in  the 
bottom,  concentric  with  the  reaction  chamber,  and  with  a 
diameter  half  that  of  the  reaction  chamber. 

This  arrangement  is  reported  to  save  floor  space  and  lead,  and 
start  remarkably  easily. 

Such  an  arrangement  is  in  service  at  the  plant  of  the  Fairmount 
Chemical  Co.,  Fairmount,  W.  V.  It  is  running  on  coal  brasses, 
which  of  course  produce  a  large  amount  of  CO2,  so  the  figures  are 


Hot  to  Scale 


FIG.  25. 


o 

o          o 
o 

Bottom 


not  of  the  value  that  they  would  be  if  the.  conditions  were  more 
nearly  standard,  but  Dr.  Thiele  expresses  himself  as  well  pleased 
with  results. 

To  briefly  cover  a  few  of  the  best  known  arrangements  of  this 
kind,  the  Lunge  Plate  Column  is  one  of  the  early  proposals. 
This  is  essentially  a  comparatively  small  lead  tower  packed  with 
stoneware  plates  spaced  a  few  inches  apart.  These  plates  have 
numerous  small  holes  in  them  so  arranged  that  holes  in  one  do  not 
occur  directly  below  those  in  the  next  above.  The  plates  have 
slightly  raised  circumferences  and  the  rims  of  the  holes  are 
also  raised  so  that  some  acid  always  lies  on  each  plate  and  drips 
down  through  the  holes  and  splashes  about  as  fresh  acid  forms 
or  is  fed  in.  This  apparatus  is  not  for  big  plants  for  size  of 
plates  is  necessarily  limited. 

The  Gilchrist  Pipe  Column  is  a  lead  tower  with  many  hori- 
zontal lead  pipes  extending  through  from  side  to  side,  both  ends 


THE  CHAMBERS  109 

being  open  to  the  air.  Circulation  of  air  through  the  pipes  gives 
some  cooling  effect  and  the  mixing  is  attained  by  the  gas  forcing 
through  between  them. 

Lead  towers  packed  with  brick  or  coke,  or  quartz,  similar  in 
construction  to  Gay  Lussac  towers  are  sometimes  used  between 
chambers.  These  may  be  used  dry  or  may  have  cool  acid  circu- 
lated over  the  packing. 

A  series  of  two  or  three  open  towers  with  neither  packing  nor 
circulation  of  acid  has  been  used. 

Chambers  are  fitted  with  steam  or  water  connections  or  both, 
for  introducing  the  necessary  water  to  make  acid  of  proper 
strength.  Steam  is  usually  put  into  each  chamber  at  two  or 
three  places  only,  as  it  spreads  well.  These  are  usually  in  the 
top,  sometimes  in  the  front  end  wall.  Water  must  be  introduced 
at  several  points  and  in  a  very  finely  divided  condition  for 
otherwise  drops  would  go  quickly  down  to  the  bottom  without 
entering  into  the  reaction.  Special  atomizing  nozzles  of  glass 
or  stoneware  or  platinum  are  made  for  the  purpose.  The  water 
for  this  purpose  must  be  filtered  and  delivered  to  the  nozzles  at 
uniform  pressure  usually  about  60  Ib. 

Steam  distributes  through  the  reacting  gases  better  than 
water  spray  unless  the  apparatus  for  introducing  the  latter  is 
carefully  taken  care  of.  Water  of  course  is  much  cheaper  to  use 
if  live  steam  has  to  be  used.  If  a  uniform  supply  of  waste  steam 
is  available  it  is  quite  acceptable.  Water  has  the  advantage 
over  steam  in  that  it  exerts  a  considerable  cooling  action  on  the 
gas  mixture  which  in  summer  particularly  is  valuable. 

In  order  that  the  operator  may  know  the  gravity  of  the  acid 
being  made  in  any  given  chamber  at  any  time,  small  gutters 
are  burned  to  the  inside  of  the  chamber  walls  at  one  or  two 
convenient  points.  A  portion  of  the  acid  running  down  the 
walls  is  diverted  by  them  to  an  opening  in  the  curtain  through 
which  it  flows  over  a  sealing  lip  into  a  small  jar  in  which  is  kept 
a  hydrometer.  By  observing  and  recording  the  hydrometer 
readings  from  time  to  time  the  operator  is  enabled  to  control 
properly  the  admission  of  steam  or  water  to  the  individual 
chamber. 

One  or  two  thermometers  are  inserted  into  each  chamber. 
If  one  only  is  used  it  is  placed  in  a  side  wall  at  the  centre  and 
about  5  ft.  above  the  working  floor.  If  two  are  used  one  is 
placed  near  each  end.  These  thermometers  are  made  with  a 


110 


AMERICAN  SULPHURIC  ACID  PRACTICE 


long  stem,  usually  about  12  in.,  below  the  graduated  portion. 
This  stem  is  turned  45°  or  90°  from  the  graduated  part  and  is 
inserted  through  a  rubber  stopper  inside  the  chamber  wall,  the 
graduated  part  being  vertical  and  conveniently  read.  Such 
thermometers  are  stock  articles  with  the  large  supply  houses. 

The  last  one  or  two  chambers  of  a  set  are  frequently  equipped 
with  bell  jars  or  sight  glasses  in  order  that  the  color  of  the  gas 
may  be  observed. 

For  drawing  off  the  acid  from  the  chamber  pans  and  for 
communication  between  them,  pipes  are  led  from  the  bottom  of 
the  pan  to  a  bo'ot  near  the  end  or  between  the  chambers,  or  small 
alcoves  are  made  on  the  pan  ends  which  are  joined  beneath  the 


FIG.  26. 

floor  by  pipes.  In  any  case  at  least  one  end  of  each  such  pipe 
should  be  accessible  for  blowing  out  accumulations  of  mud. 
Figure  26  shows  details. 

CHAMBER  VOLUME 

The  number  of  cu.  ft.  of  chamber  volume  which  must  be 
provided  for  making  a  given  tonnage  of  acid  depends  upon 
several  factors.  It  may  first  be  well  to  note  that  it  is  customary 
to  speak  of  the  performance  of  chambers  as  using  a  certain 
number  of  cu.  ft.  per  pound  of  sulphur  per  24  hours.  This 
expression  of  rating  was  brought  into  use  to  do  away  with  the 
uncertainty  that  existed  when  one  spoke  of  volume  per  unit  of 
acid.  It  was  found  that  the  manufacturer  whose  product  was 
50°  acid  often  spoke  of  his  production  in  terms  of  50°  acid  while 
he  whose  product  was  60°  used  that  as  a  basis,  and  yet  others 
had  in  mind  66°  or  even  100%  H2S04. 

In  order  to  make  common  ground  of  comparison  the  idea  of 
using  sulphur  itself  as  a  basis  has  come  into  general  use.  Even 
this  is  not  always  common  ground  as  one  man  will  reckon  on 
sulphur  contained  in  the  ore  burned,  another  on  sulphur  burned 


THE  CHAMBERS  111 

out  of  the  ore,  and  a  third  on  sulphur  in  the  acid  made.  Of 
course  only  the  last  is  correct. 

There  is  a  divergence  in  claims  of  performance  and  a  divergence 
in  performance  of  modern  acid  plants,  in  respect  of  cu.  ft.  of 
chamber  space  per  pound  of  sulphur  in  acid  made  per  24  hours, 
of  from  about  8  to  20.  An  average  of  these  two  extremes,  say 
14,  is  probably  not  far  from  the  volume  actually  used  in  most 
plants.  The  plants  which  run  on  8  or  10  cu.  ft.  per  pound  of 
sulphur  have  special  arrangements  such  as  towers  fans,  etc.,  in 
connection  with  their  chambers.  Some  plants  having  small 
plain  chambers  in  which  the  ratio  of  radiation  surface  to  volume 
is  comparatively  high  run  on  10  to  12  cu.  ft.  Some  few  plants 
have  be^n  constructed  in  recent  years  in  which  large  units — 100 
to  300  tons  60°  acid — contained  only  4  or  6  enormous  chambers. 
The  ratio  of  surface  to  volume  is  very  low — mixing,  cooling,  and 
impingment  are  largely  sacrificed,  but  construction  cost  per 
cu.  ft.  of  chamber  space  is  very  low.  In  these  plants  around 
20  cu.  ft.  per  pound  of  sulphur  was  provided  and  is  used. 

These  observations  bring  out  the  fact  that  merely  to  say  that 
a  plant  is  working  on  so  many  cu.  ft.  of  chamber  space  does  not 
determine  whether  its  performance  is  all  that  should  be  expected 
or  not.  If  two  plants  of  different  design  are  built  and  each 
costs  $500,000,  each  produces  100  tons  of  acid  a  day  with  the 
same  operating  costs,  and  one  operates  on  8  cu.  ft.  and  the  other 
on  20  cu.  ft.  the  performance  of  the  latter  is  just  as  creditable  as 
that  of  the  former. 

It  is  the  opinion  of  many  designers  that  plain  chambers  of 
moderate  size  and  simple  design  give  the  most  satisfactory 
results  all  things  being  considered. 

LEAD  SPECIFICATIONS 

One  of  the  largest  Chamber  Acid  plants  in  the  country  answers  our 
inquiry  as  follows: 

"It  has  not  been  our  practice  to  make  any  other  specification  except 
that  lead  shall  be  what  is  known  to  the  trade  as  'chemical  lead.' 

"We  have  always  purchased  this  from  the  same  company  and  the 
quality  has  been  uniform.  It  must  be  free  from  other  metals,  and 
sufficiently  ductile  to  permit  of  rolling  out  into  thin  sheets.  The 
addition  of  small  percentages  of  copper  has  been  advocated  by  some 
engineers,  but  we  have  had  no  experience  with  this  alloy.  For  the 
construction  of  acid  valves,  fans  and  other  apparatus  that  require 


112  AMERICAN  SULPHURIC  ACID  PRACTICE 

structural  strength,  we  use  a  mixture  of  chemical  lead  with  7  per 
cent  to  10  per  cent  antimony. 

LIFE  OF  LEAD 

"The  exact  life  of  lead  in  chamber  plants  cannot  be  accurately  stated, 
as  it  depends  too  much  on  local  conditions.  I  would  say  that  the  life 
is  influenced  chiefly  by  the  temperature  and  whether  or  not  scouring 
action  obtains.  We  have  had  chambers  to  run  without  interruption 
for  nearly  10  years,  but  repairs  were  made  to  various  parts  during  the 
interval." 


CHAPTER  X 
GAY  LUSSAC  TOWERS 

The  Gay  Lussac  towers  follow  the  chambers  in  the  course 
of  the  gas.  They  receive  from  the  chambers  normally  a  gas 
mixture  consisting  essentially  of  nitrogen  about  92  to  96  parts 
by  volume,  oxygen  about  4  to  8  parts  by  volume  and  the  oxids 
of  nitrogen  NO  and  NO2  from  %Q  to  1  per  cent  by  volume. 
Of  course  small  amounts  of  C02  and  other  gases  are  present 
but  ordinarily  have  no  bearing  on  the  subject.  There  are  a  few 
special  cases  where  carbonaceous  fuel  is  used  in  the  furnaces 
from  which  the  SO2  is  derived,  in  which  CO2  must  be  reckoned 
with.  These  are  unusual  and  need  not  be  considered  in  a 
general  discussion.  The  temperature  of  this  gas  entering  the 
Gay  Lussacs  is  only  slightly  above  that  of  the  atmosphere. 
The  result  desired  from  the  Gay  Lussacs  is  the  recovery  of  the 
oxides  of  nitrogen  by  absorption  in  60°  sulphuric  acid  which  is 
fed  into  them.  . 

The  Gay  Lussac  towers  then  should  be  built  of  such  material 
as  to  resist  the  action  of  comparatively  cool  60°  acid  and  gas. 
They  should  be  designed  in  such  a  way  as  to  bring  the  gas  and 
acid  into  as  intimate  contact  as  possible  and  yet  allow  reasonably 
free  passage  for  the  gas.  They  must  be  of  such  height  as  to  allow 
a  sufficient  degree  of  contact  between  gas  and  acid  to  accomplish 
substantially  a  90  per  cent  recovery  of  the  nitrogen  oxides. 

These  requirements  differ  from  those  of  the  Glover  tower  in 
the  matter  of  temperature  of  gas  and  volume.  In  the  Glover 
tower  the  gases  enter  at  temperatures  so  high  as  to  be  injurious 
to  bare  lead  and  it  is  therefore  necessary  in  constructing  a  Glover 
tower  to  provide  a  heavy  masonry  lining  wall  to  protect  the  lead 
shell.  No  such  protection  is  required  in  the  Gay  Lussac  towers 
wherein  the  gas  temperature  rarely  reaches  120°F.  The  Gay 
Lussac  tower  therefore  need  be  simply  a  well  supported  lead 
shell  completely  filled  with  packing,  excepting  of  course  the  gas 
chambers  above  and  below.  This  statement  does  not  apply  in 
those  cases  where  non-symmetrical  packing  such  as  coke  or 
quartz  is  used  because  such  material,  in  a  column  20  to  40  ft. 
s  113 


114  AMERICAN  SULPHURIC  ACID  PRACTICE 

high,  exerts  so  much  lateral  thrust  as  to  bulge  and  cut  the  lead, 
and  masonry  supporting  walls  are  necessary.  It  is  unusual  to 
use  such  packings  now.  With  the  symmetrical  packings,  bricks, 
rings  or  other  shapes,  the  weight  is  all  carried  on  the  bottom. 

Some  designers  still  build  Gay  Lussac  towers  with  lining 
walls  even  though  symmetrical  packing  is  used,  but  it  is  a  waste 
of  material  and  a  waste  of  good  absorption  space.  Also  it  is 
actually  bad  for  the  lead  shell  to  have  an  interior  wall,  in  that 
gas  gets  in  between  the  masonry  and  the  lead,  circulates  slug- 
gishly, and  the  nitrogen  compounds  oxidize  up  to  nitric  acid 
which  often  corrodes  the  lead  badly. 

With  this  exception  the  general  construction  of  the  Gay 
Lussac  towers  is  much  like  that  of  the  Glover.  A  massive 
foundation  is  put  down  of  sufficient  height  that  the  acid  issuing 
from  the  tower  pans  may  run  by  gravity  to  circulation  tanks. 
This  usually  means  on  a  level  site  that  the  top  of  the  foundation 
will  be  about  10  ft.  above  the  ground.  The  top  surface  of  this 
foundation  is  carefully  levelled  and  made  smooth  by  trowelling. 
A  sheet  of  light  lead  4  to  6  Ib.  per  square  foot  is  next  laid.  The 
edges  of  this  sheet  may  be  turned  up  a  few  inches  to  make 
a  shallow  pan  and  a  drain  pipe  put  in,  or  else  the  edges  are 
projected  a  few  inches  beyond  the  concrete  and  turned  down 
slightly  to  throw  any  acid  leakage  away  from  the  foundation. 
This  lead  is  also  turned  up  around  the  footings  of  the  columns 
of  the  framework. 

The  tower  pans  are  made  of  15  or  20  Ib.  lead  and  are  usually 
24  in.  high.  False  bottoms  of  10  Ib.  lead  are  placed  inside  over 
those  portions  of  the  bottom  on  which  the  brickwork  is  to  rest. 
The  side  sheets  of  the  tower  are  hung,  fastened  to  the  frame  and 
burned  together.  They  may  be  burned  to  the  pan  or  extend 
down  inside  it.  The  latter  method  is  not  so  bad  here  as  in  the 
chambers  as  the  acid  is  cold.  ,  However  it  wastes  lead  and  has 
no  particular  advantages.  The  side  walls  are  usually  of  10-lb. 
lead. 

Ordinarily  the  top  is  not  put  on  the  tower  till  the  brickwork  is 
in.  Through  the  open  top  the  brick  and  packing  material 
is  introduced.  It  is  perhaps  easier  and  safer  to  open  three  or 
four  holes  in  one  side  and  put  in  the  packing  through  them. 
When  the  packing  is  finished  these  holes  are  closed  by  the  lead- 
burners.  All  danger  of  bricks  falling  and  injuring  the  workmen 
is  done  away  with  if  this  plan  is  followed.  The  top  lead  is  of  the 


GAY  LUSSAC  TOWERS  115 

same  weight  as  the  side  sheets.  A  chamber  4  or  5  ft.  high  is  left 
without  packing  at  the  top  to  provide  for  the  proper  acid  dis- 
tribution and  leave  the  exit  flue  free. 

The  base  structure  for  supporting  the  packing  and  the  packing 
proper  are  substantially  as  described  under  the  Glover  Tower. 

There  should  be  on  each  Gay  Lussac  tower  a  carefully  designed 
acid  distribution  system  with  suitable  tanks  for  feeding  it.  This 
apparatus  is  described  under  Acid  Circulation. 

As  to  volume,  dimensions  and  number  of  Gay  Lussac  towers 
suitable  for  a  unit  of  given  size  a  considerable  difference  of  opinion 
seems  to  exist  if  one  may  judge  by  an  examination  of  different 
plants.  Reverting  first  to  the  classic  Lunge  we  find  Gay  Lussac 
towers  compared  in  volume  to  the  total  chamber  space  which 
they  serve.  Lunge  states  that  the  packed  volume  of  the  Gay 
Lussacs  should  be  not  less  than  1  per  cent  of  the  chamber  space 
and  better  between  2  per  cent  and  3  per  cent.  This  method  of 
proportioning  would  be  satisfactory  if  all  chamber  space  did  the 
same  work  but  such  is  not  the  case.  As  mentioned  before  some 
chamber  sets  use  20  cu.  ft.  of  space  per  pound  of  sulphur  and 
others  less  than  10  cu.  ft.  Lunge  of  course  refers  to  continental 
practice  of  several  years  ago  in  which  the  larger  amounts  of 
chamber  space  were  used.  It  is  more  pithy  in  this  day  to  pro- 
portion and  speak  of  Gay  Lussac  volumes  in  terms  of  sulphur 
made  into  acid  of  60°Be.  On  this  basis  Lunge  advocates  not 
less  than  100  cu.  ft.  of  packed  volume  per  ton  60°  acid  produced 
and  for  really  good  nitre  recovery  up  to  200  cu.  ft. 

This  range  from  100  to  200  cu.  ft.  of  packed  volume  per  ton 
60°  acid  is  about  what  is  found  in  modern  American  plants. 
Certainly  the  upper  figure  should  be  approached  but  this  is  not 
always  done.  With  Gay  Lussacs  well  proportioned  and  skill- 
fully operated  whose  packed  volume  amounts  to  200  cu.  ft.  per 
ton  of  60°  acid  made  in  the  plant,  a  recovery  of  about  90  per  cent 
of  the  nitre  can  be  made.  The  total  nitre  introduced  into  the 
modern  plant  amounts  to  25  to  30  per  cent  of  the  sulphur. 
The  loss  of  nitre  then  on  the  above  basis  amounts  to  2.5  to  3 
per  cent  of  the  sulphur. 

The  absorption  of  nitre  in  the  Gay  Lussac  towers  is  of  course 
much  more  rapid  in  the  earlier  part  than  the  late  parts.  Without 
attempting  to  formulate  or  to  give  exact  figures  it  may  be  said 
that  in  a  case  where  the  Gay  Lussac  space  was  divided  into  three 
towers  in  series  it  was  found  that  the  first  tower  retained  about 


116  AMERICAN  SULPHURIC  ACID  PRACTICE 

65  per  cent  of  the  nitre  in  the  gas  entering  it,  the  second  tower 
about  60  per  cent  of  the  remainder  and  the  third  tower  about  60 
per  cent  of  that  yet  remaining.  It  must  be  considered  that  prob- 
ably about  5  per  cent  of  the  nitre  is  not  recoverable  by  solution 
in  Sulphuric  acid.  The  above  will  then  work  out  as  follows: 

95  per  cent  total  recoverable. 
1st  Tower  65  per  cent  of    95   per  cent    =   61.75 
2d  Tower  60  per  cent  of  (95  -  61.75)    =   19.95 
3d  Tower  60  per  cent  of  (95  -  81.70)    =     7.98 
Total 89.68 

As  explained  these  figures  are  intended  simply  to  give  a  rough 
idea  of  the  relative  recovery  accomplished  by  the  different  zones 
of  Gay  Lussac  space. 

Having  decided  upon  the  volume  of  Gay  Lussac  towers  the 
number  of  towers  and  their  dimensions  are  next  calculated.  In 
order  to  secure  uniform  distribution  of  gas  and  acid  throughout 
the  packing,  it  is  well  to  make  the  horizontal  section  not  too 
large  and  consequently  the  vertical  dimension  long.  A  high 
tower  with  small  horizontal  section  makes  a  much  better  nitre 
recovery  than  a  low  tower  with  large  horizontal  section,  the 
packed  volume  in  both  cases  being  identical.  This  is  to  some 
extent  due  to  more  uniform  distribution  of  gas  and  acid  through 
the  packing,  but  in  larger  measure  to  higher  gas  velocity  and 
consequently  more  thorough  breaking  up  and  mixing  of  the  gas 
with  the  acid.  The  minimum  amount  of  horizontal  section  will 
be  dictated  by  the  pressure  necessary  to  force  the  gas  through  the 
packing.  It  is  not  desirable  to  use  high  pressures  because  the 
leadwork  of  the  flues,  fans  and  towers  will  not  stand  them.  Cer- 
tainly the  pressure  at  the  entrance  of  the  first  Gay  Lussac  should 
be  not  over  %o  or  Mo  of  an  mcn  °f  water  or  say  12  to  15  mm. 
For  ordinary  packing  a  gross  horizontal  sectional  area  of  2  sq.  ft. 
per  ton  of  60°  acid  made  should  be  provided  to  accomplish  the 
above  result.  The  total  vertical  dimension  of  the  tower  packing 
should  then  be  100  ft.  if  we  wish  to  provide  200  cu.  ft.  packed 
volume  per  ton  of  60°  acid  made.  It  is  not  practical  to  use  a 
single  tower  100  feet  high  because  of  the  difficulty  of  pumping 
acid  of  1.7  sp.  g.  to  such  an  elevation,  and  so  it  is  customary  to 
use  two  or  three  towers  in  series.  If  two  towers  be  used  the 
height  of  each  will  be  50  to  60  ft.  allowing  10  ft.  in  each  for  the 
spaces  above  and  below  the  packing.  Likewise  if  three  be  used 


GAY  LUSSAC  TOWERS  117 

the  height  of  each  will  be  43  ft.  As  the  tower  bases  will  be  at  the 
least  10  ft.  above  the  ground  and  the  feed  tanks  about  12  ft. 
above  the  top  of  the  tower  it  is  seen  that  to  the  above  figures 
some  22  ft.  must  be  added  to  get  the  vertical  distance  of  the 
acid  lift. 

It  should  be  remarked  that  many  plants  will  be  found  in  which 
the  Gay  Lussac  tower  scheme  does  not  check  up  at  all  closely 
with  the  line  of  reasoning  presented  above.  Unquestionably 
somewhat  wide  variations  can  be  made  from  it  without  sacrificing 
good  work.  The  figures  presented  are  however  quite  certain  to 
yield  excellent  nitre  recoveries. 

To  give  a  concrete  example  of  Gay  Lussac  towers  for  a  plant 
to  produce  100  tons  of  60°  acid: 

Total  packed  volume  @  200  cu.  ft.  per  ton 20,000  cu.  ft. 

Sectional  area  @  2.25 225  sq.  ft. 

20,000 
Vertical  dimension    0  0.      =  89  ft. 

_  _  •  i  , 

Using  3  towers  packed  height  each  say  30  ft.  Total  height  each 
allowing  10  ft,  for  spaces  above  and  below  packing  40  ft. 

If  the  section  be  made  square  the  horizontal  dimensions  will 
be  15  X  15.  In  the  writer's  opinion  it  would  be  better  to  make 
the  section  rectangular  say  9  ft.  X25  ft.  and  to  admit  the  gas  at 
three  points  on  the  long  side.  Such  a  plan  probably  more  fully 
utilizes  the  packing  than  the  square  section. 

The  course  of  the  gas  should  be  upward  in  all  the  towers  as 
it  has  been  demonstrated  that  a  given  tower  performs  better 
absorption  with  the  gas  going  upward,  than  downward.  The 
flues  between  the  towers  then  will  leave  the  top  of  the  first, 
descend  and  enter  the  bottom  of  the  next. 


CHAPTER   XI 
ACID  CIRCULATION 

The  acid  circulating  system  will  be  in  this  discussion  taken 
to  include  tanks,  coolers,  pumps,  pipe  lines  and  distribution 
apparatus. 

Tanks  are  almost  always  provided  at  the  top  and  bottom  of 
each  tower.  They  are  certainly  indispensable  when  intermittent 
pumping  is  used,  i.e.,  by  acid  eggs  or  montejus.  The  flow  of  acid 
into  and  out  of  each  tower  must  of  course,  be  uniform  and  con- 
tinuous and  during  the  periods  when  the  eggs  are  filling  there 
must  be  a  stock  of  acid  at  the  top  to  feed  the  towers  and  there 
must  be  a  place  at  the  bottom  to  accommodate  the  acid  issuing. 
Even  when  continuous  pumping  apparatus  such  as  centrifugal 
pumps  or  air  lifts  is  used,  it  is  advisable  to  have  tanks  both  above 
and  below,  although  in  this  case  they  need  not  be  so  large. 

Three  kinds  of  tanks  are  used  for  this  service,  viz.,  lead-lined 
wood  tanks,  lead  tanks  supported  by  skeleton  iron  framework, 
and  iron  tanks.  The  lead-lined  wood  tanks  are  most  used  and 
the  iron  tanks  least. 

Wood  tanks  are  always  of  rectangular  section  for  conven- 
ience of  framing.  Usually  they  consist  of  rather  heavy  sills  and 
caps  with  upright  posts,  strongly  put  together  with  bolts  and 
dowels.  Inside  this  frame,  2  or  3  in.  planks  are  spiked,  making 
a  smooth  and  solid  wall  all  round.  Lead  usually  10  Ib.  per  square 
foot  is  then  put  in  and  turned  over  the  top  caps  and  an  inch  or 
two  down  outside.  The  burned  seams  should  be  some  little  dis- 
tance from  the  corners  as  they  are  the  places  most  likely  to  break 
open. 

A  neat  way  of  making  a  wood  tank  frame,  particularly  for 
small  tanks  is  to  build  up  a  crib  of  2  X  4  or  2  X  6  material  as 
shown  in  Fig.  27.  This  of  course,  leaves  2-in.  strips  of  the  lead 
open  for  the  air,  but  no  bulging  of  any  moment  occurs. 

Lead  tanks  with  iron  frames  are  always  made  circular.  The 
iron  frames  consist  of  four  or  more  upright  angle  iron  pieces  with 
flat  circular  bands  or  hoops  riveted  inside.  The  number  of  hoops 
for  a  tank  4  ft.  6  in.  or  5  ft.  high  is  usually  four,  one  at  the  top, 

118 


ACID  CIRCULATION 


119 


one  near  the  middle  and  two  below  the  middle  where  the  pressure 
is  greatest.  The  dimensions  of  the  iron  parts  vary  with  the  size 
of  the  tank.  For  a  10  ft.  diameter  X  5  ft.  deep  tank,  the  angles 
would  be  about  4  X  4  X  M  and  the  bands  4  X  Y^  Ten-  or  12- 
Ib.  lead  is  used  in  tanks  of  this  type.  They  are  very  satisfactory 
if  the  details  of  design  are  correct,  and  very  neat  in  appearance. 
Iron  tanks  have  come  into  use  to  some  extent  in  the  last  few 
years  for  60°  acid.  There  is  no  particular  reason  why  they  should 
not  be  as  satisfactory  as  are  iron  tank  cars  or  storage  tanks. 
They  cannot  be  so  readily  repaired  in  case  of  leakage  as  can  lead 
tanks  but  on  the  other  hand,  for  several  years  at  least  they  are 
not  so  likely  to  leak  They  should  not  of  course,  he  used  for 
acids  much  under  60°Be. 


FIG.  27. 

Circulation  tanks  of  any  construction  are  usually  made  from 
4  ft.  6  in.  to  5  ft.  high.  This  makes  them  easy  to  look  into  and 
allows  light  construction  as  no  great  pressures  are  produced. 

The  capacities  of  circulation  tanks  vary  widely  for  plants  of  a 
given  size.  It  is  not  desirable  to  tie  up  too  great  a  tonnage  of 
acid  in  circulation  and  yet  reasonable  capacities  should  be  pro- 
vided to  carry  over  periods  in  which  minor  repairs  to  lines,  valves, 
etc.,  may  be  necessary.  It  would  seem  that  tanks  large  enough 
to  contain  at  least  two  hours'  normal  flow  should  be  provided 
at  the  top  and  bottom  of  each  tower.  At  the  bottom  of  the  Gay 
Lussac  tower  which  produces  finished  nitrous  vitriol,  somewhat 
more  space  is  desirable,  up  to  six  or  eight  hours'  flow,  say.  This 
allows  a  stock  of  nitrous  vitriol  to  be  held  which  is  highly  desirable 
in  restarting  the  acid  process  in  case  of  a  shut  down. 

It  is  a  very  good  plan  to  have  two  small  tanks  at  each  point 
instead  of  one  large  one.  If  this  is  done  one  tank  may  be  cut 
out  to  clean  or  repair  without  disturbing  operations.  The  pipe 
lines  leaving  a  circulation  tank  should  have  machined  seats  of 
hard  lead  (or  iron,  if  iron  tanks  are  used)  at  their  points  of  exit 


120  AMERICAN  SULPHURIC  ACID  PRACTICE 

from  the  tanks,  and  plugs  or  stems  to  correspond.  In  case 
valves  in  any  line  have  to  be  changed  or  the  line  opened  for  any 
reason,  the  plugs  can  be  set  and  the  flow  of  acid  stopped.  It  is 
convenient  to  have  a  washout  pipe  df  generous  size  in  the  bottom 
of  each  tank  as  well  as  the  service  line.  This  washout  is  ordi- 
narily closed  with  a  blind  flange. 

Storage  tanks  for  sulphuric  acid  are  made  of  mild  steel  plate 
with  riveted  joints.  They  are  of  circular  section,  have  flat 
bottoms  and  dome  or  conical  tops.  They  are  similar  in  general 
features  to  large  tanks  used  for  storage  of  oil,  except  that  as  the 
liquid  they  contain  has  a  high  specific  gravity  they  are  heavier 
metal.  It  is  highly  important  that  all  seams  shall  be  perfectly 
tight  because  any  leakage,  however  slight,  causes  serious  outside 
corrosion  in  a  short  time.  The  bottom  of  the  tank  should  be 
supported  on  masonry  walls  or  piers  a  short  distance  above  the 
ground  in  order  that  the  bottom  seams  can  be  inspected.  The 
pipe  for  drawing  off  the  acid  is  equipped  with  a  seat  and  plug 
or  a  long  stem  or  with  an  inside  swing  pipe  so  that  the  flow  of 
acid  from  the  tank  may  be  stopped  in  case  of  a  failure  of  a  valve 
or  pipe.  Every  storage  tank  should  have  one  or  two  manhole 
castings  with  blind  flanges  bolted  on  in  its  side  near  the  bottom 
in  order  that  the  mud  may  be  cleaned  out  of  it  from  time  to  time. 
If  such  cleaning  is  necessary  only  at  long  intervals,  say  over 
one  or  two  years,  the  mud  may  be  flushed  out  with  a  strong 
stream  of  water.  There  will  be  produced  during  the  time  of  such 
washing  acid  solutions  of  a  strength  which  attacks  iron,  but  the 
injury  done  the  tank  during  the  few  hours  required  for  washing 
out  is  negligible.  Removal  of  mud  from  a  storage  tank  by 
hand  is  a  serious  and  dangerous  task. 

The  acid  issuing  from  the  Glover  tower  is  so  hot  as  to  be  injuri- 
ous to  pipes  etc.,  and  far  too  hot  to  absorb  nitre  when  it  is  put 
over  the  Gay  Lussacs,  hence  coolers  are  necessary  at  the  base  of 
the  Glover  tower.  These  are  open-top  tanks  containing  lead- 
pipe  coils  through  which  cold  water  is  circulated. 

This  is  sometimes  augmented  by  spraying  water  on  the  outside 
of  the  tank  or  by  making  it  with  double  walls  and  circulating 
cold  water  between  them.  The  hot  acid  is  discharged  into  the 
top  of  the  tank  and  leaves  it  at  the  bottom  through  a  pipe  which 
rises  up  almost  to  the  top  again.  In  this  way  the  cooler  is 
always  kept  full  and  the  acid  takes  its  natural  course,  i.e.,  as  it  is 
cooled  it  sinks  to  the  bottom  and  runs  off. 


ACID  CIRCULATION 


121 


The  tanks  are  made  with  wood  boxes  lined  with  lead  or  with 
iron  framework,  as  described  above.  Some  times  a  brick  lining 
is  put  inside  the  lead.  If  the  tank  is  jacketed  it  is  made  with  the 
shells  heavy  enough  to  be  self  sustaining.  The  coils  are  made  of 
IJ^-in.  or  IJ^-in.  lead  pipe.  They  may  be  made  flat  spirals  or 
upright  spirals.  If  flat,  several  are  placed  superimposed.  If 
vertical,  they  may  be  of  different  diameters  and  set  concentric- 
ally or  may  be  of  the  same  size  and  set  side  by  side.  The  cold 
water  enters  at  the  bottom  and  circulates  upward  and  leaves  the 


Water 


Water 


Water  Discharge 
'Lounder 


Detail  of^cid  Discharge 


Pis  charge 
FIG.  28. 


top,  in  this  way  the  cold  water  is  brought  into  contact  with  the 
cooler  acid,  and  the  warmed  water  with  the  hot  acid.  Superim- 
posed flat  coils  are  not  to  be  recommended  bn  account  of  the 
inconvenience  of  repairing  or  replacing  them.  Uniform  upright 
coils  are  best  in  this  respect  and  give  fully  as  good  results  as 
regards  cooling.  A  sketch  of  a  cooler  with  this  type  of  coils  is 
shown  in  Fig.  28. 

Between  1  and  2  sq.  ft.  of  coil  surface  should  be  providedr 
per  ton  of  acid  per  24  hours  going  through  a  cooler  tank.    The 


122  AMERICAN  SULPHURIC  ACID  PRACTICE 

cooler  tanks  should  have  an  acid  capacity  such  that  the  acid 
will  be  in  contact  with  the  coils  from  1  hour  to  1%  hours.  For 
example,  if  the  tower  is  discharging  300  tons  of  60°  acid  per  24 
hours,  the  total  surface  of  the  pipe  coils  should  be  perhaps  450 
sq.  ft.  and  the  acid  capacity  of  the  coolers  should  total  around  15 
tons  or  285  cu.  ft.  These  proportions  may  be  varied  properly 
with  the  temperature  of  the  acid  issuing  from  the  Glover  and  the 
temperature  of  the  cooling  water.  They  work  well  if  the  former 
is  275°F.  and  the  water  60°F.,  i.e.  the  acid  will  issue  from  the 
cooler  at  a  temperature  around  70°. 

There  should  always  be  at  least  two  coolers  with  the  inlet 
launders  and  discharge  pipes  so  arranged  and  of  such  size  that 
any  one  cooler  may  be  cut  out,  emptied  and  washed  while  the 
entire  acid  stream  goes  temporarily  through  the  others.  A 
generous  washout  pipe  leading  to  the  sewer  should  be  provided 
on  each  cooler  tank. 

Pumping  sulphuric  acid  presents  difficulties  which  are  not 
encountered  in  pumping  water,  oil  and  other  familiar  liquids. 
It  is  corrosive  to  many  metals  and  it  quickly  destroys  any  packing 
material.  Hence,  any  pump  which  depends  upon  a  flexible 
packing  for  tightness  is  out  of  the  question.  Reciprocating,  or 
plunger  pumps  cannot  be  used  at  all  and  even  centrifugal  pumps 
which  involve  glands  packed  with  flexible  material  are  trouble- 
some. These  facts  have  led  to  the  almost  universal  use  of  an 
apparatus  known  variously  as  the  acid  egg  or  blow  case,  or  monte- 
jus.  The  air  lift  or  pulsometer  is  also  widely  used  and  to  an 
increasing  extent,  the  vertical  submerged  centifugal  pump. 

The  acid  egg  is  a  cast-  or  wrought-iron  vessel  provided  with 
three  openings  for  pipe  .connections.  One  of  them  which  just 
enters  the  egg  is  connected  to  the  supply  tank  and  through  it  the 
acid  enters  the  egg  by  gravity  flow.  The  second  which  also 
just  enters  the  egg,  serves  alternately  for  the  admission  of  com- 
pressed air  and  the  blow-off.  The  third  pipe  extends  almost  to 
the  bottom  of  the  egg  and  through  it  the  acid  is  forced  out  of  the 
egg  and  up  through  the  discharge  line  to  a  tank  on  top  of  the 
towers.  To  operate  this  device,  the  blow-off  valve  is  opened  to 
atmospheric  pressure  and  the  compressed-air  valve  is  closed. 
The  valve  in  the  feed  line  is  opened  and  the  egg  allowed  to  fill 
with  acid.  Next  the  valve  in  the  feed  line  is  closed,  the  blow- 
off  valve  is  closed  and  the  compressed-air  valve  is  opened.  The 
compressed  air  flows  into  the  egg  and  forces  out  the  acid  through 


ACID  CIRCULATION 


123 


the  discharge  line.  When  the  egg  is  empty  or  nearly  so,  the 
compressed  air  is  shut  off  and  the  blow-off  valve  is  opened.  When 
the  pressure  is  relieved,  the  feed  line  is  once  more  opened  and  the 
cycle  begins  again.  Figure  29  shows  a  typical  layout.  It  is 
important  that  the  blow-off  pipe  be  carried  up  above  the  level 
of  the  top  of  the  feed  tank  in  order  that  acid  may  not  run  out 
through  the  blow-off  line  when  the  egg  is  filled.  The  blow-off 
valve  is  of  acid  proof  construction.  The  arrangement  shown  is 
operated  by  hand.  A  convenient  modification  is  to  have  a  check 
valve  in  the  feed  line  instead  of  a  hand-operated  valve.  There 
have  been  many  clever  automatic  devices  developed  for  operating 
the  compressed  air  blow-off  valves.  Almost  all  of  them  depend 
upon  the  action  of  a  float  within  the  egg  to  open  and  close  the 


Acidln 


w 

e|                 °^ 

-•*' 

n 

B 

Oj 

u 

i°i 

o| 

joj 

i°i 

O| 

l°l 

JoJ 

01 

I°L 

*  Riveted  and 

"*••  W  I  P/afa 

Caulked  Joint- 

J... C.I.  Saddle 


FIG.  29. 

valves  or  ports.  The  Kestner  Automatic  Egg  was  an  early  and 
much  used  apparatus  of  this  type  but  is  probably  not  being  in- 
stalled in  this  country  now.  Descriptions  of  it  can  be  found  in 
Lunge  and  other  publications  of  several  years  ago.  Simpler  and 
more  satisfactory  automatic  valves  are  now  being  made  by  the 
Schulte  and  Koerting  Co.  and  the  Monarch  Manufacturing 
Works,  both  of  Philadelphia.  Both  of  these  consist  essentially 
of  a  small  lead  casing  in  which  a  float  works.  When  the  egg  is 
empty  the  lower  part  of  this  float,  which  is  conical,  seats  in  a 
depression  whose  sides  are  pierced  by  ports  connected  with  high- 
pressure  air,  and  closes  them.  When  the  acid  rises  up  about  the 
float  it  rises  off  these  ports  and  its  upper  surface  seats  against 
the  orifice  of  the  blow-off  pipe,  thus  admitting  air  to  the  egg  and 
closing  the  blow  off.  The  acid  is  blown  out  through  the  usual 
discharge  pipe  and  when  all  out  the  air  also  escapes  and  the 


124  AMERICAN  SULPHURIC  ACID  PRACTICE 

pressure  within  the  egg  decreases  to  such  an  extent  that  the  float 
drops  and  closes  the  air  inlet  and  opens  the  blow  off. 

It  is  to  be  considered  that  any  automatic  apparatus  requires  a 
certain  amount  of  attention  to  keep  it  in  order.  Also  that  the 
flows  of  acid  into  and  out  of  tanks  must  be  kept  under  observa- 
tion. One  man  can  easily  operate  a  large  battery  of  hand- 
operated  eggs  and  the  latter  are  almost  trouble  proof.  It  is  a 
question  therefore,  whether  or  not,  everything  considered,  auto- 
matic apparatus  is  more  satisfactory  than  hand-operated.  As 
regards  economy  of  air  and  power,  the  matter  is  largely  one  of  the 
care  with  which  the  apparatus  is  operated  and  maintained.  To 
be  sure,  a  careless  pumpman  can  waste  a  great  deal  of  air.  On 
the  other  hand  an  automatic  valve  which  is  not  working  properly 
can  do  the  same.  Air  pumping  at  best,  is  a  very  inefficient 
method  of  using  power. 


c  T   a 


FIG.  30. 

Eggs  for  pumping  sulphuric  acid  were  formerly  almost  always 
made  of  cast  iron,  but  as  the  size  of  chamber  units  increased  and 
the  volumes  of  acid  to  be  raised  correspondingly  increased,  it 
became  desirable  to  make  very  large  eggs.  In  cast-iron,  these 
would  be  enormously  heavy  and  expensive  and  so  the  egg  made 
of  wrought-iron  plates,  riveted  together  was  evolved.  Such 
eggs  are  now  in  use  of  a  capacity  up  to  250  cu.  ft. 

Cast-iron  eggs  are  made  in  several  different  shapes;  one  of 
which  is  shown  in  Fig.  30.  Usually  only  two  pieces  are  necessary 
to  make  up  the  complete  egg,  i.e.,  there  is  just  one  flanged  joint 
to  be  made.  This  joint  is  made  tight  with  a  gasket  of  10-  or 
12-lb.  sheet  lead.  Three  flanged  nipples  are  cast  integral  with 
the  egg  body.  In  some  cases  a  depression,  or  well,  is  made 
below  the  nipple  designed  for  the  discharge  pipe  and  the  latter 
dips  into  it,  the  idea  being  to  get  all  the  acid  out  of  the  egg  at  each 
pumping.  This  is  a  rather  unnecessary  refinement  as  in  a  short 
time  the  bottom  of  the  egg  accumulates  some  sediment  and  the 
end  of  the  discharge  pipe  is  in  a  "  well"  in  this  sediment  anyway. 


ACID  CIRCULATION  125 

It  is  unwise  to  line  iron  eggs  with  lead  as  some  minute  opening 
in  the  latter  is  sure  to  develop.  When  this  occurs  the  lead  is 
very  soon  blown  away  from  the  iron  by  the  action  of  the  air  and 
soon  the  iron  is  exposed  to  the  action  of  the  acid  anyway.  Cast 
iron  eggs  of  ample  thickness,  up  to  2  in.  last  for  many  years  if 
only  acids  near  60°Be.  are  handled  in  them. 

Wrought-iron  eggs  should  be  made  of  as  high  grade  wrought- 
iron  plate  as  can  reasonably  be  obtained.  The  usual  design  is 
shown  in  Fig.  29.  A  cast-iron  saddle  is  riveted  on  one  side  and 
this  covered  with  a  plate  on  which  are  cast  the  usual  nipples. 
This  plate  is  bolted  to  the  saddle  which  also  serves  as  a  manhole. 
As  mentioned,  eggs  of  this  type  are  especially  suitable  in  the 
large  sizes. 

For  elevating  acid  of  50°  or  less,  iron  eggs  are  not  suitable  as 
too  much  corrosion  results.  For  this  service  the  air  lift  is  much 
used.  It  is  a  satisfactory  device  but  it  uses  a  very  large  amount 
of  power  and  has  some  other  disadvantages  which  make  it  less 
suitable  than  eggs  for  pumping  60°  acid. 

In  its  simplest  form,  the  air  lift  is  a  U-shaped  pipe  with  one 
limb  longer  than  the  other  and  with  a  pipe  for  carrying  com- 
pressed air  entering  the  long  limb  just  above  the  turn  at  the 
bottom.  The  acid  to  be  elevated  is  fed  into  the  short  limb  and 
the  long  limb  discharges  into  an  elevated  tank.  To  operate, 
acid  is  allowed  to  flow  into  the  pipe  until  the  acid  is  level  in  both 
limbs,  then  the  compressed  air  line  is  opened  somewhat.  The 
air  produces  an  emulsion  or  mixture  of  acid  and  air  bubbles. 
When  sufficient  air  has  become  mixed  with  the  acid  that  the 
column  of  mixture  filling  the  long  limb  is  lighter  than  the  column 
of  solid  acid  in  the  short  limb,  a  flow  is  established.  To  get  good 
results  with  an  air  lift  the  long  limb  should  be  not  more  than 
two  times  the  length  of  the  short  limb  and  it  is  preferable  to 
make  the  ratio  1J^  to  1  when  elevations  permit. 

Ordinarily,  as  in  elevating  acid  from  the~*fehambers  to  the  top 
of  the  Glover  tower,  the  elevations  are  such  that  a  single  air  lift 
cannot  be  arranged  above  ground,  i.e.,  the  height  of  the  chambers 
above  the  ground  is  very  much  less  than  one  half  the  height  of 
the  Glover  tower  top  above  ground.  In  order  to  get  a  sufficient 
length  of  the  short  limb  of  the  lift  a  pit  or  well  is  sunk  into  the 
ground  and  the  pipe  extended  down  into  it.  While  this  is  a  very 
common  procedure,  it  sometimes  leads  to  considerable  trouble 
and  serious  loss  of  acid  in  case  of  leakage.  In  a  well  particularly, 


126 


AMERICAN  SULPHURIC  ACID  PRACTICE 


inspection  is  impossible  and  a  leak  may  exist  for  some  time 
before  it  is  suspected.  To  repair,  it  is  necessary  to  draw  the 
pipes  out. 

In  order  to  do  away  with  the  well,  or  pit,  the  multi-stage 
lift  was  developed.     This  simply  amounts  to  putting  together 


D     O 


H0       O 


FIG.  31. 


FIG.  32 


several  simple  lifts  of  increasing  height  until  the  final  elevation 
is  reached.  It  has  the  advantage  of  being  all  above  ground  and 
in  sight.  It  is  necessary  of  course,  to  so  adjust  the  admission 
of  air  to  each  lift  that  it  will  take  away  all  the  acid  which  the 
preceding  lift  delivers  to  it.  Once  properly  set,  an  air  lift  goes 


Section  A-A 


on  elevating  acid  without  supervision.  It  would  seem  from 
the  theory  of  this  method  of  lifting  acid  that  the  air  should  be 
forced  in  through  many  small  orifices  rather  than  a  single  larger 
one.  We  find  in  practice  both  arrangements  and  from  the 
author's  experience,  it  must  be  said  that  there  does  not  appear 


ACID  CIRCULATION 


127 


to  be  any  great  difference  in  general  results.  Details  of  two 
common  schemes  are  shown  in  Figs.  31  and  32.  At  the  top  of 
the  long  limb  it  is  necessary  to  provide  a  box,  or  pot,  to  receive 
the  mixture  of  acid  and  air,  in  which  the  two  can  separate  and 
from  which  the  acid  can  run  into  a  tank  or  another  lift  and  the 
air  escape.  A  baffle  of  some  kind  prevents  acid  from  splashing 
out  of  the  air  exit.  Figure  33  shows  such  an  arrangement. 

From  the  standpoint  of  economy  of 
power  and  supervision,  the  centrifugal 
pump  would  appear  to  be  the  best  way 
of  elevating  acid.  Concerning  power, 
there  has  never  been  any  question  as 
to  the  economy  over  air  pumping. 
Maintenance  of  centrifugal  pumps  has 
for  years  been  the  thing  that  has  pre- 
vented their  general  use  and  the  stuffing 
box  where  the  shaft  enters  the  case  the 
particular  point  of  trouble.  Sixty  de- 
gree acid  rapidly  destroys  rubber,  or 
flax,  or  any  of  the  ordinary  flexible  ma- 
terials used  for  packing.  Many  metallic 
packings  and  combinations  of  metals 
with  the  flexible  materials  have  been 
tried  with  indifferent  success.  Special, 
and  often  highly  ingenious  glands  have 
been  devised  but  so  far  as  the  author 
knows,  all  of  these  leave  much  to  be 
desired. 

A  centrifugal  pump  which  approaches 
the  problem  from  a  different  angle  has 
been  put  into  use  during  the  past  three 
or  four  years  and  appears  to  be  very 
satisfactory.  This  is  a  pump  with  a 
vertical  shaft.  The  whole  pump  is 
placed  in  the  tank  from  which  the 

acid  is  to  be  pumped  or  in  a  boot  connected  with  it.  The 
shaft  extends  a  short  distance  up  above  the  top  of  the  tank  or 
boot  and  is  driven  by  a  belt  or  direct  connected  motor.  The 
stuffing  box  trouble  is  entirely  sidestepped.  This  pump  is 
shown  in  Fig.  34.  One  of  these  pumps  working  in  60°  acid  has 
been  under  the  author's  personal  observation  for  more  than 


FIG.  34. 


128 


AMERICAN  SULPHURIC  ACID  PRACTICE 


a  year,  during  which  time  not  a  cent  has  been  expended  for 
repairs.  To  give  an  idea  of  power  consumption,  it  may  be  said 
that  one  of  these  pumps  equipped  with  a  5  H.P.  motor  elevates 
about  250  tons  60°  acid  per  24  hours  to  a  height  of  about  90  ft. 
The  vertical  pump  has  no  particular  advantage  of  course,  over 
the  horizontal  pumps  in  the  matter  of  power. 

The  pipes  used  for  conveying  acid  from  one  part  of  the  appa- 
ratus to  another  are  mostly  of  lead.  They  are  joined  together 
and  to  lead  tanks  by  burning.  When  lead  pipes  are  joined  to 
iron  apparatus  or  when  the  joints  are  not  permanent  as  in  case 
of  valves,  iron  flanges  are  used.  The  method  of  making  a  flanged 
joint  is  shown  in  Fig.  35.  Oval  flanges  with  two  bolts  are 
suitable  for  small  pipe,  but  for  larger  sizes,  2-,  3-,  4-in.  or  larger, 
the  4-  and  6-hole  circular  flanges  are  better. 


FIG.  35. 

Iron  pipe  is  very  successfully  used  in  certain  places  in  an 
acid  plant.  For  example,  the  lines  carrying  60°Be.  acid  from  the 
eggs  or  centrifugal  pumps  to  the  tanks  at  the  tower  tops  can 
much  better  be  of  iron  than  of  lead.  These  lines  often  have  to 
sustain  pressures  of  75  to  90  Ib.  per  sq.  in.  If  they  are  of  lead, 
they  gradually  swell  and  grow  thin  and  sometimes  suddenly 
split  open  and  deluge  a  large  area  with  acid.  Iron  pipes,  partic- 
ularly extra  heavy  iron  pipes,  last  for  years  in  this  service  and 
when  they  do  fail  they  give  ample  warning  by  first  showing 
minor  leaks.  They  are  best  made  up  with  flanged  joints  using 
lead  gaskets,  so  that  any  piece  may  be  replaced  without  taking 
down  a  long  run  of  pipe.  Turns  should  be  made  by  bending  the 
pipe  in  fairly  long  radius  arcs  instead  of  using  fittings.  Another 
advantage  which  iron  pipe  possesses  is  its  superior  rigidity. 
Lead  pipe  is  likely  to  be  badly  shaken  and  eventually  cracked  by 
the  blow  off  of  eggs,  while  iron  pipe  can  be  very  securely  bolted 
to  framework  to  prevent  such  shaking. 


ACID  CIRCULATION 


129 


As  the  discharge  lines  from  eggs  or  centrifugal  pumps  deliver 
acid  at  rather  high  velocity,  provision  must  be  made  at  the 
points  of  delivery  to  prevent  splashing.  This  is  done  by  running 
the  pipes  into  splash  eggs  or  covered  boots  as  shown  in  Fig.  36. 
If  the  form  shown  in  sketch  A  is  used,  it  can  well  be  made  of  cast 
iron. 

It  is  necessary  to  have  some  method  of  knowing  how  much 
acid  each  top  tank  has  in  it,  in  order  that  the  pumping  may  be 
done  at  proper  times  and  the  flows  maintained.  Three  schemes 
of  merit  are  in  use,  viz.,  floats,  pneumatic  indicators  and  electrical 
indicators. 

In  the  float  system  a  hollow  lead  float  rests  on  the  acid  in 
the  tank  and  has  fastened  to  it  a  chain  or  cable  or  wire  which 
runs  over  pulleys  to  a  convenient  point  near  the  pumps  where 


Sploi&h  Egg 


Splash  6oot 


Fio.  36, 


it  is  fastened  to  a  weight  running  on  a  graduated  board.  As 
the  acid  rises  and  falls  the  float  moves  the  weight  up  and  down 
and  indicates  the  level.  This  works  well  enough  but  it  is  rather 
cumbersome. 

In  the  pneumatic  scheme  a  bell  or  pot  is  set  on  the  bottom  of 
the  tank.  A  small  bore  metal  tube  is  connected  to  it  and  runs  to 
a  mercury  gauge  at  the  desired  point.  A  compressed  air  line 
or  a  small  air  pump  communicates  with  this  tube.  Air  is  admit- 
ted to  the  tube  until  all  the  acid  is  blown  out  of  the  latter  and 
out  of  the  bell  in  the  tank  and  then  shut  off.  The  head  of  acid 
in  the  tank  then  compresses  the  air  in  the  bell  and  the  tube 
and  the  pressure  exerted  is  indicated  in  the  mercury  gauge  which 
is  graduated  to  show  the  stage  of  acid  in  the  tank.  Absolute 
tightness  of  this  apparatus  is  imperative  as  the  most  minute 
leak  renders  it  unreliable. 

Electrical  indicators  are  simplest  and  best.  An  ordinary  direct 
or  alternating  light  circuit  is  employed.  Lead  rods  of  varying 
lengths  are  hung  in  the  tank  to  be  indicated.  An  incandescent 
lamp  on  a  board  is  provided  at  the  desired  point  of  observation 


130 


AMERICAN  SULPHURIC  ACID  PRACTICE 


to  correspond  to  each.  One  side  of  the  light  circuit  is  connected 
to  one  socket  terminal  and  the  other  side  to  the  lead  rod.  The 
metal  of  the  tank  is  connected  with  the  other  socket  terminal. 
When  the  acid  in  the  tank  is  in  contact  with  the  lead  rod  the 
current  flows  through  the  acid  and  lights  the  lamp.  When  the 
acid  falls  below  the  rod,  the  circuit  is  opened  and  the  light  goes 
out.  It  is  customary  to  use  at  least  two  rods  and  lights  to  each 
tank  or  as  many  levels  as  desired  can  be  shown  by  using  more. 
It  is  a  good  plan  to  provide  a  bell  or  horn  connected  to  all  the 
tanks  to  call  attention  to  any  tank  which  is  in  danger  of 
overflowing.  Figure  37. 


IIP  V.  Light  Circuit 


Acid  Tank 


FIG.  37. 


DISTRIBUTION 

The  fundamental  purpose  of  the  towers,  both  Glover  and  Gay 
Lussac,  is  to  bring  acid  and  gas  into  as  intimate  contact  as 
possible.  This  makes  it  necessary  to  distribute  or  sprinkle  the 
acid  over  the  entire  area  of  the  tower  packing  as  uniformly  as 
possible  so  that  in  flowing  down  through  the  tower  the  surfaces  of 
the  packing  material  may  be  covered  with  a  constantly  changing 
film  of  the  acid.  There  are  two  general  methods  of  doing  this. 
One  of  these  divides  the  total  acid  stream  into  many  small 
streams  before  entering  the  tower  tops  and  introduces  each 
stream  through  a  small  pipe,  or  opening.  The  other  plan  is  to 
divide  the  total  acid  stream  into  a  few  comparatively  large 
portions  which  are  further  broken  up  and  distributed  inside 
the  tower  by  spray  nozzles  or  splash  plates.  The  former  method 


ACID  CIRCULATION 


131 


is  older  and  probably  more  used  than  the  latter.  It  works 
very  well  if  the  acid  is  clean  and  the  tower  small.  In  some 
of  the  large  units  built  in  this  country  in  recent  years,  the  towers 
have  such  great  areas  that  the  first  described  plan  involves  a 
tremendous  number  of  feed  pipes  and  the  second  method  is  more 
suitable. 

There  are  many  ways  in  which  the  division  of  the  acid  and 
introduction  into  the  tower  can  be  accomplished.  Two  of  these 
are  shown  in  Figs.  38  and  39.  In  Fig.  38  the  acid  is  delivered 
into  a  central  compartment  A.  Around  A  are  small  compart- 


Oagcor 
Piano  Box 


FIGS.  38  and  39. 


ments  B,  from  each  of  which  a  luted  pipe  runs  to  some  point  in 
the  tower  top.  Acid  overflows  from  A  into  B  over  lips  on  the 
partition.  These  lips  are  all  dressed  to  the  same  level  so  that 
equal  volumes  of  acid  flow  over  all.  This  apparatus  is  made  of 
lead  and  may  of  course,  be  square  or  rectangular  or  any  desired 
shape. 

In  Fig.  39  the  internal  compartment  is  omitted,  the  acid 
being  delivered  into  the  shallow  pan  from  which  the  small  pipes 
run  directly  to  the  top  of  the  tower.  These  pipes  project  up 
into  the  pan  an  inch  or  two  and  are  covered  by  cups  whose  lower 
edges  are  notched.  The  equal  distribution  of  the  acid  depends 
upon  having  each  of  these  upstands  precisely  level  and  exactly 


132 


AMERICAN  SULPHURIC  ACID  PRACTICE 


the  same  height.  This  is  a  difficult  thing  to  determine  and 
maintain  and  this  apparatus  is  consequently  not  to  be  recom- 
mended. In  any  form  of  distributor  box  the  individual  streams 
should  be  in  sight  at  all  times  and  any  inequalities 
easily  corrected. 

With  either  of  these  arrangements  or  any  similar 
ones,  the  small  streams  of  acid  simply  trickle  down 
into  the  tower  and  on  to  the  packing.  Some  de- 
signers consider  it  essential  to  provide  one  of  these 
small  streams  for  each  square  foot  of  packing  area, 
i.e.,  for  a  tower  10  ft.  X  10  ft.  there  would  be  100 
small  streams.  Other  designers  consider  one  stream 
sufficient  for  6  or  7  sq.  ft.  It  can  be  appreciated 
that  if  one  pursues  a  middle  course  in  the  matter, 
the  number  of  individual  pipes  required  for  a  large 
tower  of  say  250  or  300  sq.  ft.  area,  is  very  great,  costly  to 
install,  and  rather  troublesome  to  keep  in  order,  especially  if 
the  acid  carries  some  sediment. 

The  second  described  general  method  of  distribution,  i.e., 
by  introducing  a  few  comparatively  large  streams  which  are 
sprayed  out  inside  the  tower,  has  much  to  recommend  it.  The 
original  division  of  the  main  stream  of  acid  can  be  carried  out  in 


FIG.  40. 


( 

2 

1 

TTTT 

0      0 

U   U 

11 

u  u 

U   U 

LI 

F 

3ld 

n 

c 

-f 

j 

Section  C-C 


Top  of 
Tow<sr 


Splash  Plate 


A 


u  o  u u rrruu  u 

Elevation 


\ 


Gacje  Plate  A-A 


FIG.  41. 


much  the  same  way  as  shown  in  Fig.  38.  The  secondary  com- 
partments are  much  fewer  in  number.  Each  pipe  enters  the 
tower  top  through  a  luted  opening  and  has  burned  to  its  end  a 


ACID  CIRCULATION  133 

spraying  device.  The  simplest  of  these  devices  is  the  splash 
plate  as  shown  in  Fig.  40.  This  is  a  casting  of  hard  lead.  Other 
more  elaborate  spray  nozzles  of  acid  resisting  material  are  also 
suitable.  Such  sprayers  can  be  depended  upon  to  quite  uni- 
formly distribute  acid  over  a  4-  or  5-ft.  circle,  at  a  distance  of 
4  ft.  below  the  nozzle.  At  6  ft.  below  the  nozzle  they  will  spray 
a  6-  ft.  circle.  It  is  important  that  each  pipe  should  originate 
in  an  individual  compartment  so  that  if  an  obstruction  occurs 
in  any  sprayer  it  will  be  immediately  known  by  the  correspond- 
ing compartment  filling  up.  The  nozzle  can  than  be  withdrawn 
through  the  luted  hole  and  cleaned.  The  distribution  afforded 
by  such  an  arrangement  is  even  better  than  that  given  by  the 
multiple  pipe  scheme,  and  it  is  obviously  much  simpler,  and 
cheaper  to  build  and  less  trouble  to  keep  in  order.  Figure  41 
shows  a  convenient  layout  embracing  the  described  features  and 
including  a  gauging  compartment. 

INTRODUCTION  OF  WATER  INTO  THE  CHAMBERS 

While  this  subject  does  not  properly  come  under  acid  circula- 
tion, it  may  well  be  discussed  at  this  point. 

Water  is  put  into  the  chambers  as  steam  or  as  finely  divided 
liquid.  If  there  is  available  to  the  plant  an  unused  supply  of 
exhaust  or  by-product  steam,  or  if  there  is  no  fairly  pure  water 
available,  it  is  proper  to  use  steam  in  the  chambers.  Otherwise 
atomized  water  should  be  used  because  it  is  better  for  the  acid- 
making  process  and  it  involves  no  fuel  expense.  The  only  cost 
is  for  driving  a  very  small  pressure  pump. 

When  steam  is  used  it  is  ordinarily  introduced  at  two  or  three 
points  in  the  top  of  each  chamber,  more  rarely  at  a  point  in  the 
front  end  wall.  A  convenient  arrangement  is  to  run  the  steam 
main  under  the  floor  of  the  working  aisles  and  to  carry  up  one  or 
two  risers  alongside  each  chamber  to  the  top  where  they  run  in  to 
the  points  of  introduction.  A  cock  or  throttle  valve  is  placed  in 
each  riser  4  ft.  above  the  working  floor.  A  pointer  mounted  on 
the  wrench  or  handle  swings  in  front  of  a  graduated  arc  and 
enables  the  operator  to  judge  how  much  of  a  change  he  is  making 
when  it  is  necessary  to  change  the  flow.  Iron  pipe  is  used  to 
carry  the  steam  to  within  2  or  3  ft.  of  the  point  of  admission  to 
the  chamber  then  a  lead  pipe  is  flanged  to  it,  bent  to  form  a  trap 
and  its  end  burned  into  the  chamber.  Low  pressure  steam  even 


134 


AMERICAN  SULPHURIC  ACID  PRACTICE 


so  low  as  2  or  3  Ib.  can  be  used,  but  the  pressure  should  be 
uniform  at  all  times. 

In  using  liquid  water,  the  introduction  is  done  through  many 
small  nozzles  rather  than  through  two  or  three  large  ones.  There 
are  two  reasons  for  this.  One  is  that  control  of  the  amount  of 
water  admitted  into  a  chamber  is  accomplished  by  completely 
opening,  or  completely  closing  a  number  of  the  supply  pipes. 
The  other  that  even  well  atomized  water  does  not  spread  out 
into  a  very  large  volume  of  the  reacting  gas  and  so»the  sprays 
must  be  numerous  to  assure  each  portion  of  the  chamber  of  its 
proper  amount  of  water. 

The  spray  nozzles  used  in  this  country  are  made  of  hard 
lead  with  platinum  liners,  or  of  stoneware  or  glass.  The  former 


Rubber 


.  Platinum 
Liner 


In  terior  PIPCQ 


FIG.  42. 


are  much  more  expensive  than  the  latter  though  they  usually 
last  much  longer.  With  platinum  prices  where  they  now  are, 
one  can  buy  eight  or  ten  stoneware  or  glass  nozzles  for  the  price 
of  one  platinum  nozzle.  The  principle  used  in  all  nozzles  is  to 
produce  a  swirl  in  the  water  stream  just  before  it  leaves  the 
orifice.  This  is  done  in  several  ways,  two  of  which  are  illustrated. 
When  working  properly  the  water  issues  in  a  cone  shaped  sheet 
which  breaks  into  innumerable  small  drops.  Figure  42. 

As  all  the  passages  in  these  nozzles  are  small,  the  areas  rang- 
ing up  to  1  sq.  m.m.,  it  is  essential  that  the  water  entering  the 
nozzles  be  very  free  from  solid  impurities  or  they  soon  become 
plugged  up.  The  water  should  not  carry  more  than  small 
quantities  of  salts  in  solution  because  when  a  nozzle  is  not  used 
for  some  hours  the  water  remaining  in  it  evaporates  and  salts 
deposit  and  choke  it. 


ACID  CIRCULATION 


135 


Pressures  used  on  this  equipment  are  usually  around  60  Ib. 
per  sq.  in.  at  the  nozzle.  It  is  important  that  the  pressure 
what-ever  it  may  be  shall  be  kept  uniform  within  a  few  pounds. 

There  are  two  or  three  manufacturers  in  this  country  who  have 
made  up  excellent  combinations  of  apparatus  for  filtering  and 
pumping  water  for  chamber  sprays.  Figure  43  shows  the  arrange- 
ment of  an  individual  spray  nozzle  with  cock  and  strainer,  lute, 


Strainer 


Wafer 


FIG.  43. 

etc.  The  water  is  filtered  through  sponges  and  uniform  pressure 
maintained  in  the  lines  by  an  electric  plunger  pump  with  relief 
valve.  In  addition  to  this  it  is  advisable  to  use  a  strainer  as 
shown  just  preceeding  each  individual  nozzle  to  catch  any  pipe 
scale  or  anything  that  escapes  the  main  filter.  In  cold  weather 
when  there  is  danger  of  the  small  spray  lines  freezing,  a  steam 
pipe  leading  into  the  supply  tank  warms  the  water. 


CHAPTER  XII 
INTRODUCTION  OF  NITRE 

The  recovery  of  the  nitre  in  the  chamber  process  is  never 
complete.  The  average  loss  is  probably  from  3  per  cent  to 
4  per  cent  (96  per  cent  NaN03)  of  the  sulphur  in  the  acid  actually 
produced.  It  is  necessary  then  to  introduce  into  the  plant 
per  24  hours  from  15  to  20  Ib.  of  new  nitre  for  each  ton  of  60° 
acid  produced. 

While  it  is  the  custom  to  speak  of  introducing  "  nitre,"  the 
thing  actually  wanted  and  done  is  to  introduce  into  the  gas 
mixture  the  gaseous  oxides  of  nitrogen.  This  is  done  in  two  ways. 
The  first  and  probably  most  frequent  is  to  decompose  sodium 
nitrate  by  sulphuric  acid  and  heat  in  cast  iron  pots  placed  in  a 
flue  between  the  furnaces  and  the  Glover  Tower.  The  heat  of 
the  furnace  gases  is  depended  on  to  produce  the  reaction.  Some- 
times the  nitre  pots  are  placed  in  brick  settings  alongside  the 
gas  flue  and  heat  is  supplied  by  means  of  coal  fires  beneath  them. 
The  nitric  acid  vapor  is  led  immediately  into  the  gas  flue  however. 

The  other  plan  is  to  make  liquid  nitric  acid  in  a  separate 
plant  and  introduce  it  into  the  top  of  the  Glover  tower. 

In  either  case  the  chemical  reactions  and  the  end  results  are 
the  same.  The  .reactions  which  take  place  in  the  nitre  pot 
whether  it  is  in  the  gas  flue,  in  a  separate  setting  or  in  the  nitric 
acid  plant  are  these: 

NaN03  +  H2S04  =  NaHS04  -f  HN03 
2NaN03  +  H2S04  =  Na2S04  +  2HN03 

The  nitric  acid  comes  off  as  a  vapor.  The  acid  sodium  sulphate 
and  normal  sodium  sulphate  remain  in  the  pot  as  a  liquid  mass 
and  are  tapped  off  from  time  to  time.  If  the  pot  is  in  or  near 
the  gas  flue  the  nitric  acid  vapor  mingles  with  the  hot  burner 
gas  and  reacts  with  it  substantially  as  follows : 

2HNO3  +  3SO2  +  2H20  =  3H2S04  +  2NO 

In  the  nitric  acid  plant  the  nitric  acid  vapor  is  cooled  suffi- 
ciently to  condense  it  to  liquid  HN03.  This  when  introduced 

136 


INTRODUCTION  OF  NITRE 


137 


into   the   Glover  tower  is  reacted  upon  in  the  same  way,  i.e., 
H2SO4  and  NO  are  formed. 

Nitre  pots  are  used  in  the  gas  flue  and  are  of  very  simple  design. 
They  are  generally  of  rectangular  shape,  open  at  the  top  and 
have  a  spout  at  one  end  for  tapping  off  the  nitre  cake.  Figure 
44  shows  a  conventional  design.  These  pots  have  capacities 
ranging  from  about  3  to  4  cu.  ft.  up  to  20  cu.  ft.  Larger  sizes 
become  difficult  to  handle  when  they  break  and  have  to  be  re- 
placed. The  small  sizes  accommodate  25  to  50  Ib.  charges  and 
the  larger  up  to  200  Ib.  The  thickness  of  metal  is  from  2  to  4 
in.  The  matter  of  material  is  somewhat  puzzling.  Some  foun- 
dries claim  great  superiority  for  their  special  cast  iron  formulas. 


FIG.  44. 

I  have  seen  pots  of  these  special  irons,  which  also  cost  a  special 
price,  give  very  poor  service,  and  some  have  very  long  lives. 
The  same  can  be  said  of  pots  made  of  good  ordinary  cast  iron  by 
local  foundries.  Probably  design  and  care  in  pouring  have  as 
much  to  do  with  the  life  of  a  pot  as  special  metals.  Pots  usually 
fail  by  cracking  or  going  through  flaws  rather  than  by  actual 
corrosion. 

The  number  of  pots  which  should  be  provided  varies  with  the 
size  of  the  unit  somewhat,  but  should  be  never  less  than  two  and 
preferably  more. 

This  on  account  of  the  desirability  of  having  as  nearly  uniform 
evolution  of  nitric  acid  vapor  as  possible,  and  to  carry  over  the 
periods  of  changing  a  broken  pot  for  a  new  one.  If  the  unit  is  of 
50  tons  60°  capacity,  the  normal  amount  of  nitre  introduced  per 


138  AMERICAN  SULPHURIC  ACID  PRACTICE 

24  hours  will  be  from  750  to  1,000  Ib.  There  will  be  times  when 
more  than  that  will  have  to  be  potted  for  a  few  hours  so  it  will 
be  well  to  have  pot  capacity  to  introduce  at  the  rate  of  2,000 
Ib.  per  24  hours.  Two  hours  per  charge  is  the  minimum 
time  which  should  be  allowed  for  the  decomposition  of  the  size 
charges  ordinarily  used.  If  therefore  two  pots  are  provided  each 
should  be  able  to  handle  1,000  Ib.  per  24  hours  in  12  charges  or 
83^<j  Ib.  per  charge  and  should  have  a  volume  of  about  10  cu. 
ft.  If  three  pots  are  provided  they  should  be  of  7  cu.  ft.  volume 
or  if  four  pots  of  5  cu.  ft.  volume. 

The  pots  are  supported  well  above  the  bottom  of  the  flue  on 
beams,  in  order  that  the  hot  gas  may  play  freely  around  them. 
The  spout  extends  out  through  the  wall  a  short  distance.  If  the 
pots  are  small  and  the  span  for  the  beams  is  not  long  ordinary  I 
beams  are  used  for  support  and  last  very  well.  In  case  large 
pots  are  used  and  the  flue  is  10  or  15  ft.  wide,  deep  cast  channels 
filled  with  reinforced  concrete  stand  up  splendidly. 

Charging  of  the  pots  with  nitre  and  acid  can  be  done  from  top 
of  the  flue  or  from  the  side.  In  many  respects  charging  from 
the  top  is  more  satisfactory.  It  does  away  with  the  rather 
laborious  handling  of  a  heavy  loaded  charging  ladle  and  it  puts 
charging  and  tapping  at  different  levels  which  is  desirable.  If 
both  operations  are  done  on  the  same  floor  the  cake  pans  or 
launders  are  most  inconvenient  to  work  over.  The  nitre  is  put 
into  the  pot  through  a  cast  iron  pipe  with  bell  top  if  the  charging 
is  done  from  the  top.  If  the  charge  opening  is  in  the  side  of  the 
flue  a  large  scoop  or  ladle  with  a  sufficiently  long  handle  is  used. 
The  acid  is  fed  in  from  a  measuring  pot  or  box  through  a  heavy 
cast  iron  pipe.  The  special  high  silicon  irons  and  also  fused 
silica  are  being  used  for  these  pipes  of  late  as  even  a  heavy  cast 
pipe  does  not  last  long.  Figure  45  shows  an  arrangement  of  nitre 
pots  in  a  flue. 

The  nitre  cake  is  usually  tapped  off  into  shallow  pans,  allowed 
to  cool  and  harden,  then  broken  up  and  removed.  When  condi- 
tions permit  and  there  is  no  use  for  the  nitre  cake,  a  simple  means 
of  disposal  is  to  tap  into  a  launder  in  which  a  stream  of  water  runs, 
when  the  molten  cake  dissolves  and  is  flushed  away.  Several 
ways  have  been  devised  for  closing  the  spout  after  the  charge 
has  been  tapped.  A  plate  and  screw  clamp  is  sometimes  used. 
Or  the  end  of  the  spout  is  machined  out  to  take  an  iron  plug. 
Sometimes  wooden  plugs  are  used.  If  the  spout  is  long  outside 


INTRODUCTION  OF  NITRE 


139 


the  flue  a  ball  of  mud  will  be  sufficient.  It  is  well  to  use  a  scheme 
which  does  not  depend  too  much  on  machined  surfaces  for 
tightness. 


I — >g   Section  A-A 

Charge  F\oor<, 


Y/////////////////////////////. 
Section  B-B 

FIG.  45. 


POTTING  WITH  FUEL 

While  the  general  features  of  the  method  just  described,  i.e., 
in  placing  nitric  pots  in  the  flue  and  utilizing  the  heat  of  the  SO2 
gas  to  effect  the  decomposition  of  the  nitre,  would  seem  the  best 
and  most  economical  possible  arrangement,  it  has  some  drawbacks 
which  are  so  annoying  that  many  acid  plants  are  now  equipped 
with  nitre  pots  in  independent  settings  and  fired  with  fuel. 
When  this  plan  is  used  the  operator  can  have  at  all  times  just  the 
degree  of  heat  he  wishes  to  decompose  his  nitre.  If  the  process 
has  become  badly  disturbed  by  some  breakdown  or  stop  he 
can  decompose  the  extra  nitre  the  emergency  demands  and  get 
into  normal  condition  quickly.  The  weakness  of  the  flue  potting 
lies  in  the  fact  that  just  at  those  times  when  an  unusually  large 
amount  of  nitre  should  be  potted  the  flue  is  cold,  e.g.,  when  start- 


140 


AMERICAN  SULPHURIC  ACID  PRACTICE 


ing  up  the  plant  after  a  shutdown  or  when  any  unusual  occurrence 
disturbs  the  flow  of  hot  furnace  gas  about  the  nitre  pots.  In 
choosing  between  flue  pot  and  independent  pots  the  source  of  the 
S02  must  be  regarded.  If  the  sulphur  supply  is  in  the  form  of  a 
uniform  high-grade  pyrites  which  will  make  a  hot  gas  and  allow 
long  campaigns  with  the  roasting  furnaces,  flue  potting  is  quite 
proper.  If  the  gas  is  cold  or  if  it  is  an  unreliable  metallurgical 
by-product  gas,  independent  fuel  fired  pots  probably  are  most 
economical.  Fuel  cost  is  not  a  very  important  consideration  as 
with  well  designed  settings  a  ton  of  ordinary  soft  coal  will  decom- 
pose 3,000  to  4,000  Ib.  of  nitre. 

The  best  form  of  pot  for  fuel  fired  settings  is  shown  in  Fig.  46. 
This  is  a  modern  retort  such  as  is  used  in  nitric  acid  work.  It 
is  simple  and  strong  and  is  a  design  which  has  been  very  generally 
adopted  of  late  years. 


totted 


FIG.  46. 


An  ingenious  plan  used  in  connection  with  fuel-fired  pots  is 
used  at  the  works  of  the  Tennessee  Copper  Co.  The  retorts  are 
substantially  standard  nitric  acid  casting  as  shown  in  Fig.  46. 
The  nitre  is  fed  in  continuously  by  means  of  a  conveyor  and  at  the 
same  time  the  proper  amount  of  sulphuric  acid  for  decomposing 
it  is  run  in.  Both  nitre  and  acid  may  be  varied  as  desired  to 
meet  the  demands  of  the  acid  process.  When  a  retort  is  filled 
up  to  a  certain  point  with  fused  nitre  cake  it  is  tapped.  There 
are  several  retorts  in  the  battery  and  the  introduction  of  nitric 
acid  vapor  into  the  flue  is  continuous.  This  arrangement  is 
described  in  an  article  by  A.  M.  Fairlie  in  Chemical  and  Met- 
allurgical Engineering  of  September  25,  1918. 

At  some  sulphuric  acid  works  liquid  nitric  acid  is  made  in  a 
separate  plant  and  the  nitric  acid  is  introduced  as  needed  into 
the  Glover  tower.  A  comparatively  recent  modification  of  this 


INTRODUCTION  OF  NITRE  141 

scheme  is  to  make  instead  of  straight  nitric  acid,  mixed  acid, 
i.e.,  a  mixture  of  nitric  and  sulphuric  acids. 

In  either  case  the  nitre  retorts  are  the  same  and  are  about  as 
shown  in  Fig.  46.  Other  forms  of  retort  and  setting  are  to  be 
found  in  some  of  the  older  plants,  but  the  larger  and  more  en- 
lightened manufacturers  of  nitric  acid  seem  to  have  come  to  the 
conclusion  that  the  form  shown  is  most  satisfactory. 

In  making  straight  nitric  acid  the  condensation  of  the  vapor 
to  liquid  is  effected  in  what  is  known  as  the  Hart  condenser. 
It  consists  essentially  of  a  pair  of  upright  manifolds  of  stoneware 
or  high  silicon  iron  with  glass  tubes  between  them.  The  glass 
tubes  are  cooled  by  trickling  cold  water  over  them.  The  final 
condensation  of  nitric  vapor  and  recovery  of  the  most  of  the 
lower  oxides  of  nitrogen  is  done  by  passing  the  gases  through 
several  stoneware  towers  in  series.  A  counter  current  stream 
of  water,  then  weak  nitric  acid  is  advanced  over  the  towers.  The 
liquid  nitric  acid  made  is  received  and  stored  in  glass  or  stone- 
ware vessels.  It  is  possible  to  use  with  fair  success  iron  or  lead 
tanks  if  only  strong  nitric  acid  be  put  into  them  and  if  they  are 
kept  tight  from  air  leakage.  The  high  silicon  irons  can  be  used 
with  success  for  containing  nitric  acid  of  any  strength. 

The  nitric  acid  made  in  this  way  is  conveyed  to  the  top  of  the 
Glover  tower  sometimes  by  elevating  the  glass  carboys  containing 
it,  sometimes  by  pumping  it  up  through  stone  or  special  iron 
pipe  lines.  More  rarely  it  is  mixed  with  sulphuric  acid  and  the 
mixed  acid  then  handled  in  any  apparatus  suitable  for  sulphuric 
acid.  This  mixing  of  nitric  and  sulphuric  acid  must  be  done  in  a 
closed  vessel  provided  with  cooling  coils  as  it  fumes  badly 
otherwise. 

The  handling  of  straight  nitric  acid  especially  in  large  quanti- 
ties is  rather  troublesome  and  this  fact  led  to  the  development  of 
the  plan  of  making  mixed  acid  directly,  which  will  now  be  de- 
scribed. Mixed  acid  as  mentioned  can  be  handled  in  lead  or  iron 
apparatus  with  very  little  more  wear  and  tear  than  straight 
sulphuric  acid  causes. 

The  plant  for  making  mixed  acid  directly  consists  of  retorts 
similar  to  those  used  when  making  straight  nitric  acid.  The 
nitric  acid  vapor  issuing  from  them  is  conducted  through  pipes 
of  silicon  iron  into  a  small  tower  of  acid-proof  masonry  construc- 
tion packed  with  acid-proof  bricks  or  shapes,  over  which  cold 
sulphuric  acid  of  60°Be.  or  higher  strength  is  circulated.  The 


142 


AMERICAN  SULPHURIC  ACID  PRACTICE 


nitric  acid  vapor  is  condensed  and  a  warm  mixture  of  nitric  and 
sulphuric  acids  issues  into  a  cooler  whence  it  is  pumped  up  and 
again  introduced  into  the  tower.  The  operation  is  exceedingly 
simple  and  gives  a  high  recovery.  The  product  containing  up  to 
20  per  cent  HNO3  is  contained  and  pumped  in  lead  apparatus. 
Its  volume  is  such  that  it  is  very  nicely  controlled  in  introducing 
it  into  the  Glover  tower.  The  Fig.  47  shows  an  installation  in 
which  4,000  Ib.  of  nitrate  of  soda  is  comfortably  handled  in  an 
eight  hour  shift.  The  fuel  used  amounts  to  about  900  Ib.  ordi- 


Coohrs, 


Elevation 
FIG.  47. 

nary  bituminous  coal  per  ton  of  nitre.  The  recovery  is  96  per 
cent  or  better.  Some  of  these  plants  have  been  operating  at 
least  3  years.  Except  for  charging  the  retorts  the  operation  is 
conducted  by  one  man. 

In  the  writer's  opinion  this  last  described  method  is  the  most 
satisfactory  and  economical  way  of  handling  the  matter  of  getting 
the  nitre  into  the  chamber  process. 

It  should  be  mentioned  that  a  water  solution  of  nitrate  of  soda 
is  used  to  a  limited  extent  in  the  Glover  tower  and  in  the  cham- 


INTRODUCTION  OF  NITRE  143 

bers  as  a  means  of  nitre  introduction.  It  is  a  plan  which  has  the 
serious  disadvantage  of  fouling  the  acid  with  sodium  sulphate: 
if  the  acid  is  to  be  used  for  the  manufacture  of  fertilizer  this  is  no 
particular  drawback.  If  more  than  a  small  proportion  of  the 
total  necessary  nitre  is  put  into  the  Glover  tower  as  a  regular 
procedure  in  this  way  it  very  soon  makes  trouble  in  that  pipe 
lines  and  valves  become  obstructed  and  the  tanks  and  coolers 
fill  up  with  it.  As  an  emergency  measure  to  tide  over  a  few  days 
when  for  some  reason  the  regular  source  of  nitrogen  oxides  is  out 
of  commission  a  solution  of  this  kind  can  be  used  in  the  Glover 
without  serious  results.  Certainly  though  a  few  days  is  the 
limit.  If  the  solution  be  introduced  into  the  chambers  and  the 
chamber  acid  is  drawn  off  for  use  in  making  acid  phosphate  or 
some  other  use  in  which  sodium  sulphate  is  not  objectionable, 
very  little  trouble  results.  In  any  event  it  is  unusual  to  use  a 
nitrate  solution  as  anything  more  than  as  in  an  auxiliary,  or  a 
temporary  way  of  putting  nitrogen  oxides  into  a  chamber  system. 

NO  FROM  AMMONIA  OXIDATION 

About  30  per  cent  of  the  European  acid  plants  are  supplying 
the  oxides  of  nitrogen  to  their  chambers  by  oxidizing  ammonia 
and  introducing  the  gas.  So  far  but  one  plant  in  this  country, 
that  of  the  American  Cyanimid  Co.,  at  Warners,  New  Jersey,  has 
used  this  process,  which  gave  them  splendid  results.  It  is  not 
in  operation  at  the  present  time,  as  nitrogen  from  Chile  saltpeter 
costs  less  than  from  ammonia  now. 

In  January,  1919,  the  British  Ministry  of  Munitions  issued  a 
booklet  on  "  The  Oxidation  of  Ammonia  Applied  to  Vitriol  Cham- 
ber Plants. "  This  is  the  most  complete  publication  on  the  sub- 
ject, and  I  will  quote  from  it  very  freely. 

Mr.  W.  S.  Landis,  of  the  American  Cyanimid  Co.,  has  furnished 
the  following  information  regarding  their  New  Jersey  installa- 
tion. 

In  their  process  of  oxidation  the  platinum  gauze  is  heated  by  a 
current  of  electricity,  instead  of  depending  upon  the  heat  of  the 
reaction  entirely.  Of  course  the  current  costs  money,  but  the 
operation  is  so  free  from  trouble  of  any  kind,  the  labor  required 
practically  negligible,  and  the  product  so  uniform,  that  opinion 
differs  as  to  the  best  practice.  (Though  it  will  be  noted  in  all 
(so  far  as  I  know)  reports  on  this  subject  that  when  results  have 


144  AMERICAN  SULPHURIC  ACID  PRACTICE 

been  wanted  electrical  heating  of  the  catalyzer  was  practiced.) 
At  Warners  an  oxidation  unit  was  set  up  under  each  chamber, 
and  the  operator  looked  in  as  he  went  by.  The  gas  was  con- 
trolled by  a  2-in.  valve,  and  the  plant  ran  steadily,  with  no  ad- 
justment beyond  change  of  quantity  of  NO  made,  as  the  condition 
of  the  chambers  demanded  it,  which  adjustment  simply  meant 
open  or  close  the  2-in.  valve. 


Electrical  Co. 

'Cotter list  Unit  Frame 


FIG.  48. 

Outside  of  the  ease  of  operation,  stronger  acid  may  be  made. 
Both  denitration  and  nitre  potting  absorb  heat,  which,  if  not 
required  for  other  purposes,  may  be  utilized  in  the  Glover  to 
concentrate.  At  Warners  this  was  done.  The  nitric  oxides  from 
the  converters  were  fed  to  the  Glovers,  all  the  heat  that  was 
saved  from  the  potting  went  to  concentrating,  and  the  result 
was  a  constant  return  of  61°Be.  acid,  which  often,  for  long  periods, 


INTRODUCTION  OF  NITRE  145 

stayed  up  to  62°,  and  occasionally  reached  62.5° — with  complete 
denitration — which  is  pretty  fair  chamber  acid. 

A  patent  on  this  subject,  U.  S.  Patent  #1,173,524,  was  issued 
on  Feb.  29,  1916. 

It  is  necessary  to  introduce  the  nitric  acid  through  the  roof  of 
the  Glover  or  chamber,  as  otherwise  the  acid,  running  down 
the  side  walls  will  quickly  destroy  the  lead. 

The  British  Ministry  of  Munitions  standard  converter  consists 
of  an  upper  and  a  lower  cone,  of  aluminum,  the  small  ends  of  the 
cones  being  flanged  to  the  inlet  and  outlet  pipes,  the  large  ends 
also  being  flanged,  but  to  the  catalyzer  frame.  The  internal 
section  of  the  catalyzer  frame,  was  about  4-in.  X  6-in.  (that  at 
Warners  was  larger),  and  was  simply  a  pair  of  aluminum  flanges 
between  which  the  platinum  wire,  gauze-wire  being  0.065  (.003") 
in.  mm.,  square  mesh,  80  mesh  per  inch — was  held  in  place  and 
insulated  by  mica  and  asbestos.  The  English  used  two  gauzes  in 
each  frame,  held  apart  by  silica  rods,  the  lower  gauze  alone  having 
silver  terminals.  When  electric  current  is  not  used  to  heat  the 
gauze,  three  or  four  gauzes  are  necessary. 

Ninety  per  cent  to  95  per  cent  efficiency  of  oxidation  will  be 
attained  without  electric  heating  of  the  gauze,  and  98  per  cent 
with  the  current. 

The  capacity  is  1.5  tons  of  HNOs  per  square  foot  of  converter 
cross  section  per  24  hours. 

The  aluminum  used  in  this  construction  must  be  very  pure; 
and  either  mica  or  clear  silica  must  be  used  for  the  peep  holes. 

The  catalyst  container  must  fit  tight.  Any  air  leaks  may  be 
luted  with  a  mixture  of  asbestos  powder  and  thick  water  glass. 
Allow  this  paste  to  set  before  heating  the  catalyzer. 

The  following  precautions  are  essential  in  handling  the  catalyst : 

1.  Great  care  should  be  taken  that  the  platinum  gauzes  are 
absolutely  clean.     They  are  boiled  in  pure  concentrated  hydro- 
chloric acid  and  rinsed  in  distilled  water  before  fitting,  and  should 
on  no  account  be  touched  with  the  fingers  afterwards  or  otherwise 
soiled. 

2.  The  box  containing  the  catalyst  as  sent  from  the  makers 
should  not  be  opened  except  immediately  before  fitting. 

3.  Fitting  should  be  done  in  a  clean  room  free  from  dust,  not 
on  any  account  in  a  workshop,  and  the  fitter  should  have  clean 
hands  and  clothes. 

4.  It  is  essential  that  the  greatest  possible  care  be  taken  to 
10 


146  AMERICAN  SULPHURIC  ACID  PRACTICE 

keep  the  gauzes  clean  while  the  catalyst  unit  is  being  fitted  to 
the  converter.  If  the  completed  converter  is  not  at  once  con- 
nected to  the  inlet  and  outlet  pipes,  the  apertures  of  the  lower 
cone  and  bend  pipes  at  the  top  should  be  closed  with  corks  to 
keep  out  dust  until  this  is  done. 

As  the  electrical  resistance  of  the  gauze  is  low,  the  current  must 
be  low  voltage,  but  high  in  amperage.  The  maximum,  or  start- 
ing, current  for  a  4-in.  X  6-in.  gauze  is  12  volts,  300  amperes. 

The  mixture  of  air  and  ammonia  may  be  supplied  to  the  con- 
verters in  either  of  two  ways: 

1.  By  producing  air  and  ammonia  gas  separately,  and  mixing 
them  in  the  proper  proportions — 1  vol.  NH3  to  7.5  vols.  air — in 
an  aluminum  mixing  chamber,  with  tangential  inlets  and  baffle- 
plates. 

2.  By  passing  a  stream  of  air  through  aqueous  ammonia  in  a 
suitable  apparatus. 

The  second  method  is  by  far  the  better,  and  will  alone  be 
described. 

Purified  ammonia  liquor,  20  to  25  per  cent.  NH3,  ''free  from 
sulphur/'  is  the  source  of  the  ammonia.  It  is  fed  at  the  proper 
rate  to  an  ammonia  still,  and  there  met  by  low  pressure  steam 
blown  in  at  the  bottom,  either  directly  or  through  coils,  and  a 
current  of  air.  Ammonia  gas  is  liberated,  mixed  with  the  right 
proportion  of  gas  for  oxidation,  and  if  the  top  of  the  column  is 
kept  cool,  the  gas  is  fairly  dry.  Moisture  has  no  influence  upon 
the  oxidation,  but  is  liable  to  condense  in  the  filters  and  impair 
their  efficiency.  Iron  pipe,  fitted  with  red  lead  and  oil,  may  be 
used  up  to  the  filters. 

This  still  should  work  uniformly  and  with  little  attention,  and 
not  be  liable  to  breakdowns.  It  should  have  a  low  steam  con- 
sumption, which  depends  upon  its  being  kept  hot  below  and  cool 
above.  It  should  deliver  ammonia,  or  air  and  ammonia,  at  a 
definite  rate. 

The  kind  of  ammonia  available  and  the  amount  required  will 
of  course  influence  the  design. 

Where  the  amount  required  is  small  the  ammonia  may  be 
generated  by  boiling  ammonium  sulphate  or  ammonium  chloride 
with  milk  of  lime  in  an  iron  boiler  with  a  reflux  cooler,  with  a 
small  balancing  gas  holder  between  the  boiler  and  the  converter. 
This  method  would  be  useful  at  coke  ovens  or  gas  works,  where 
such  salts  are  by-products.  It  has  the  additional  advantage 


INTRODUCTION  OF  NITRE 


147 


that  the  ammonia  is  pure,  as  there  is  no  sulphur.  On  a  large 
scale  ammoniacal  liquor  is  more  economical.  Gas  liquor  should 
not  be  used  directly,  because  of  the  impurities. 

An  ammonia  still  of  Brunner,  Mond  &  Co.  is  shown  (Fig.  49). 
Purified  ammonia  liquor  of  25  per  cent  is  run  in  at  such  a  speed 


Liquor  Lev<fl 
Orifice  Valve, 


Samp/e 
Cock 


Sfeam 


|7b  Converter 

^Gff&  Sample 
Cock  r 


mple  Cccfr 


'Steam 


,-Safeh/  Lute 

*  for  Cons  tant  Head 


•-TI — 


FIG.  49. 


tha-t  the  top  compartment  is  kept  at  8  per  cent  to  9  per  cent 
ammonia,  and  20°  to  22°C.  The  bottom  compartment  is  heated 
to  95°  to  100°C.  to  exhaust  the  ammonia.  Air  is  passed  at  the 
proper  rate,  and  t*he  mixture  through  a  slag-wool  or  glass-wool 


148 


AMERICAN  SULPHURIC  ACID  PRACTICE 


filter.     A  little  steam  is  necessary  in  the  filter  before  the  con- 
verter to  avoid  condensation. 

The  United  Alkali  Co.  replaces  the  bubbling  tower  with  a  tall 
coke  tower.  Steam  and  air  are  introduced  as  before,  but  ammo- 
nia liquor  is  introduced  at  a  point  two-thirds  up  the  tower.  The 
upper  portion  of  the  tower  thus  acts  as  a  cooler  and  gas  filter, 
and  no  further  filtration  is  necessary.  This  is  also  shown 
(Fig.  50).- 

Liquor  from 
'Ammonia  Tank 

.  2 Sigh f  Glasses 
\:Y/itn  Nick<?l  Gauze 
nfor  Filtering 


~Gla&s>  Measuring  Apparatus 
Ammonia  Inlef 


6  "Castlron  Pipes 
Lagged with  Magrte&ia 


|  j   Temp.50°C. 

3Pi'p<?&  Packed  wifh 
Hard  Coke  3  "Cubes 

w'lth  Magnesia    / 

Plate 
•z"Leael  Pipe 


Swivet  Joint  Exit1 
Water  Pipe  for 
'Controlling  Depth 

CI.WaterLute 
a  Blow-off  for  Air 


H  Lead  Pipe 

\Airfiain 


FIG.  50. 

Air  pressure  depends  upon  the  type  of  apparatus  used,  but 
should  not  fall  below  5  Ib.  per  sq.  in.  The  air  must  be  pure  and 
free  from  dust;  if  the  plant  is  near  sulphur  burners  of  any  kind 
the  air  must  be  purified  by  passing  through  a  lime  box.  There 
must  be  an  oil  trap  after  the  blower.  The  air  must  be  metered — 
the  Builders'  Iron  Foundry,  Providence,  Rhode  Island,  furnishes 
good  meters.  After  filtration  iron  pipes  must  not  be  used — 
aluminum,  stoneware,  or  glass.  The  glass-wool  filtering  medium 
will  probably  need  renewing  every  month,  as  it  fills  up  with  dust. 
Moisture  can  be  kept  out  by  introducing  a  little  steam  to  prevent 
condensation. 

The  apparatus  is  started  by  switching  on  the  current  and  heat- 
ing up  the  gauze  to  visible  redness.  The  mixture  of  air  and 


INTRODUCTION  OF  NITRE  149 

ammonia  is  then  admitted  at  a  slow  rate,  until  the  catalyzer  is 
uniformly  dull  red  hot  (650°C.),  then  the  rate  is  increased  to  the 
maximum,  the  current  being  reduced  as  necessary.  Very  little 
further  attention  is  required  for  weeks  of  running.  If  the  gauze 
gets  too  hot  the  heating  current,  or  the  proportion  of  ammonia 
in  the  mixture,  or  both,  should  be  reduced. 

When  electric  heating  is  not  used  the  plant  is  started  by  heating 
the  gauze  to  redness  with  a  hydrogen  flame,  turning  on  the  air 
and  ammonia  mixture  full,  and  removing  the  flame,  after  which 
the  window  is  bolted,  into  place. 

New  platinum  gauzes  are  somewhat  inactive,  and  should  first 
be  "activated"  by  passing  at  a  fairly  slow  rate  a  mixture  with  an 
excess  of  oxygen,  say,  1  vol.  NH3  to  ten  vols.  air,  and  putting  on 
full  current  till  the  gauzes  are  heated  BRIGHT  red  (800°  to 
900°C.)-  After  an  hour  or  two  the  platinum  becomes  activated, 
and  the  white  fumes  of  ammonium  nitrite  and  nitrate  leaving 
the  converter  (after  cooling)  change  into  clear  red  fumes  of 
oxides  of  nitrogen.  When  this  occurs  the  current  is  reduced 
and  the  ammonia  brought  up  to  the  ratio  of  one  to  7.5  air. 

If  electrical  heating  is  not  used,  start  with  the  ordinary  gas 
mixture. 

If  spots  show  on  the  heated  gauze  and  do  not  disappear  rapidly, 
the  catalyzer  must  be  taken  to  pieces,  the  gauze  boiled  in  pure  hy- 
drochloric acid,  and  the  catalyzer  reassembled.  If  the  gauzes  heat 
up  unevenly  it  is  usually  a  sign  that  the  wire  is  too  small,  and  the 
unit  must  be  replaced.  If  in  the  activation  any  unevenly  heated 
places  are  left  they  will  take  a  long  time  to  finally  become  active. 

The  gases  leave  the  converter  at  about  400°C..  They  consist 
of  NO,  steam,  nitrogen,  and  a  slight  excess  of  air.  The  converter 
reaction  is  as  follows: 

4NH3  +  502  =  4NO  +  6H20. 

At  this  temperature  the  gas  is  colorless,  as  the  secondary  oxida- 
tion of  NO  to  NO2  has  not  begun. 

The  gases  may  be  used  with  or  without  cooling. 

Without  cooling,  the  gas  is  conveyed  through  a  lagged  alumi- 
num pipe,  or  if  slightly  cooled  through  a  stone-ware  pipe,  to  the 
Glover  tower,  chamber,  or  dust  catcher  of  the  system.  The 
temperature  must  stay  high  enough  to  prevent  water  condensa- 
tion in  the  main.  There  must  be  no  pressure  possibilities  that 
burner  gas  could  back  up,  in  case  of  breakdown. 


150  AMERICAN  SULPHURIC  ACID  PRACTICE 

» 

If  the  burner  gas  does  back  iip  to  the  gauze  it  will  rapidly 
become  poisoned,  and  will  have  to  be  removed  and  boiled  in 
hydrochloric  acid.  Therefore  it  is  better  to  have  the  gas  enter 
at  a  point  where  there  is  a  slight  suction,  as  in  the  Glover  tower. 

If  the  gas  is  cooled  it  is  passed  to  a  condensing  cooler,  where 
about  70  per  cent  of  the  water  produced  in  the  reaction  is  sepa- 
rated. If  the  cooling  is  performed  sufficiently  rapidly  the  con- 
densate  will  contain  from  1  per  cent  to  5  per  cent  of  the  total 
oxides  of  nitrogen  as  nitrous  and  nitric  acid,  and  any  trace  of 
ammonia  (0.05  per  cent  to  0.25  per  cent)  which  may  have  escaped 
oxidation.  This  is  the  result  from  a  very  efficient  cooler-up 
to  25  per  cent  of  the  oxides  of  nitrogen  may  be  in  the  condensate. 
The  cooler  may  consist  of  a  silica  spiral,  connected  directly  with 
the  bend  on  the  converter  hood,  by  suitable  asbestos  packing, 
and  cooled  by  water.  A  spiral  of  10  turns  of  fused  silica  S-pipes, 
the  turns  2'-0"  in  diameter,  the  pipe  %Q-m.  thick  and  IJ^-in. 
in  diameter,  will  do  the  work.  The  condensate  may  be  collected 
in  a  stoneware  Woulff  s  bottle,  and  then  drawn  off  to  the  Glover's ; 
or  it  may  run  direct  to  the  Glover. 

The  cooled  gases,  at  about  30°  to  50°C.,  now  brown  with  oxida- 
tion from  NO  to  NC>2,  pass  through  stoneware  pipes  with  a 
stoneware  stop  cock  if  desired,  and  with  down  pitch  towards  the 
point  of  entry,  to  the  chamber  system. 

Remember  that  hot  gases  may  cause  warping  at  the  point  of 
entry,  and  provision  must  be  made  for  it. 

An  advantage  of  using  a  cooler  is  the  better  analytical  check 
on  the  process.  Tests  on  the  condensate  for  unconverted  am- 
monia should  be  made  from  time  to  time  to  check  up  the  working 
of  the  converter. 

If  there  is  more  than  one  Glover  to  be  supplied  it  is  better  to 
have  a  small  independent  converter  for  each,  rather  than  have  one 
larger  one  try  to  supply  several,  as  uniform  distribution  is  very 
difficult  to  get. 

The  accompanying  table  shows  the  quantity  of  ammonia  that 
must  be  oxidized  to  replace  any  given  quantity  of  nitre  (NaN03). 
If  the  consumption  of  nitre  varies  the  converter  may  be  run 
below  capacity — it  may  be  run  down  to  25  per  cent  of  capacity 
at  100  per  cent  efficiency,  and  will  run  well  at  15  per  cent.  One 
of  the  great  advantages  of  this  system  is  its  uniform  running, 
and  this  should  be  taken  advantage  of  if  possible,  by  keeping  the 
rest  of  the  plant  going  at  a  uniform  rate. 


INTRODUCTION  OF  NITRE 
TABLE  5 


151 


Metric  tons  of  H2SO4 

Grams  of  ammonia  required  per  hour,  if 

Sulphur 

(100%)  produced  per 

nitre  consumption  be  taken  as  per  cent 

burned 

day  of  24  hours 

of  the  sulphur  burned,  per  cent 

Tons 
per  day 

95%  plant 
efficiency 

98%  plant 
efficiency 

0.5% 

1% 

2% 

2.5% 

3% 

.265 

.77 

.792 

10 

20 

40 

50 

60 

.53 

1.55 

1.584 

20 

40 

80 

100 

120 

1.06 

3.1 

3.17 

40 

80 

160 

200 

240 

2.12 

6.2 

6.35 

80 

160 

.     320 

400 

480 

6.6 

19.25 

19.8 

250 

500 

1,000 

1,250 

1,500 

15.85 

46.2 

47.5 

600 

1,200 

2,400 

3,000 

3,600 

26.4 

77.0 

79.2 

1,000 

2,000 

4,000 

5,000 

6,000 

I 

Up  to  3,000  g.  NH3  per  hour,  use  1-4-in.  X  6-in.  converter. 
Above  3,000  g.  NH3  per  hour,  use  2-4-in.  X  6-in.  converter. 


ANALYSIS 

The  analytical  control  of  oxidization  of  ammonia  is  of  the  utmost 
importance,  and  considerable  difficulty.  With  the  methods 
here  given  the  efficiency  of  any  particular  converter  cannot  be 
determined  closer  than  3  per  cent.  This  is  sufficiently  accurate 
for  works  operations. 

Determination  of  Ratio  NH3:Air  before  oxidation 

The  method  consists  in  aspirating  a  known  volume  of  the  air- 
ammonia  mixture  through  a  sufficient  quantity  of  standard 
sulphuric  acid  colored  with  methyl  orange  or  cochineal,  contained 
in  a  wash  bottle  connected  with  an  aspirator.  A  Winchester 
bottle  of  water  is  placed  between  this  and  the  aspirator,  just  to 
equalize  the  gas  pressure  in  the  inlet  tubes  to  the  converter,  so 
that  no  gas  bubbles  through  the  acid  until  the  aspirator  is 
started. 

The  quantity  of  acid  is  sufficient  to  neutralize  exactly  0.1  g.  of 
NH3.  The  indicator  end  point  is  quite  sharp,  and  experiments 
show  that  the  absorption  of  ammonia  is  complete  with  a  single 
wash  bottle.  Each  experiment  should  be  conducted  at  such  a 
rate  as  to  last  about  10  minutes,  and  be  repeated  every  20 
minutes.  An  alternative  method  is  to  use  a  larger  volume  of 


152 


AMERICAN  SULPHURIC  ACID  PRACTICE 


standard  acid  in  two  wash  bottles,  to  aspirate  for  a  longer  time, 
say  half  an  hour,  and  titrate  back  with  standard  alkali. 

A  typical  experiment  gave  1.13  liters  of  water  aspirated  (i.e., 
1.13  1.  of  air  in  the  air-ammonia  mixture)  to  0.1  g.  of  NH3. 
This  gives  a  ratio  vol.  NH3:vol.  air  of  0.116,  which  is  about  the 
ratio  for  conversion  of  ammonia  to  N02  (0.114). 

Determination  of  ratio  oxidized  NH3:Air,  after  oxidation. 

An  aliquot  part  of  the  oxides  of  nitrogen  and  air,  from  the 
converter,  taken  from  a  T-tube  after  the  cooler  (see  Fig.  51) 
is  aspirated  through: 


Off  A  In  let- 


Water  Collector 


'Compensator 
Aspirwtvr 

-Measure 


FIG.  51, 


1.  A  Drechsel  wash-bottle  containing: 

100  c.c.  distilled  water, 
20  c.c.  N/Na202  solution, 
20  c.c.  H2O2  solution  (20  volumes). 

2.  A  Drechsel  wash-bottle  containing: 

50  c.c.  distilled  water, 

10  c.c.  N/Na2O2  solution, 

10  c.c.  H2O2  solution  (20  volumes). 

The  N/Na2O2  is  prepared  by  adding  78  g.  Na202  to  1  kg. 
powdered  ice  in  small  quantities  at  a  time,  with  stirring:  then 
adding  1  liter  distilled  water  and  filtering  through  glass-wool. 


INTRODUCTION  OF  NITRE  153 

It  is  kept  in  a  bottle  with  a  capillary  tube  through  the  cork  to 
allow  the  traces  of  O2  to  escape. 

3.  A  10-bulb  tube  containing: 

5  c.c.  N/10  potassium  permanganate  solu- 
tion. 
10  c.c.  50  per  cent  H2SO4. 

All  connections  are  made  with  ground  joints,  a  stopcock  being 
inserted  at  the  point  where  the  gas  sample  is  taken  from  the  T- 
tube,  as  shown  in  the  Fig.  51.  The  aspiration  is  effected  by 
means  of  water  dropping  slowly  from  an  aspirator  bottle  (about 
1  liter  per  hour)  into  a  measuring  cylinder,  and  1,500  c.c.  of 
water  are  collected;  the  experiment  thus  lasts  90  min. 

The  two  drechsel  wash-bottles  (1)  and  (2)  are  then  emptied  into 
two  250  c.  c.  Erlenmeyer  flasks,  the  bottles  being  then  washed, 
out  with  distilled  water  and  the  liquid  in  the  flasks  titrated 
separately  with  standard  H2SO4,  using  litmus  as  indicator,  and 
boiling  if  necessary.  The  end  point  is  taken  at  the  change  blue 
to  purple,  and  not  blue  to  red,  on  account  of  the  hydrolysis  of 
the  nitrous  acid.  This  end  point  is  easily  recognized  with  a 
little  practice.  Methyl  orange  is  useless  on  account  of  the 
action  upon  it  of  the  nitrous  acid,  but  Sodium  Alizarine  Sul- 
phonate  ("  Alizarin  Red.  I.  W.  S.,  Hochst")  has  been  used  with 
very  satisfactory  results.  The  contents  of  the  permanganate 
bubbler  are  washed  out  into  an  Erlenmeyer  flask,  treated  with 
a  slight  excess  of  N/10  oxalic  acid,  warming  if  necessary,  and 
the  excess  of  oxalic  acid  titrated  back  with  permanganate.  It 
is  assumed  that  the  reduction  of  the  permanganate  is  due  to 
NO,  and  the  NH3  equivalent  of  this  is  calculated  as  follows: 

2NO  +  30  =  N2O5, 

that  is,  2NO  (calculated  as  NH3)  requires  3  atoms  or  6  equiva- 
lents of  oxygen,  i.e.,  60,000  c.c.  N/10KMnO4:  i.e.,  34  g.  NHs  = 
60,000  c.c.  KMnO4. 

/.I  c.c.  N/10KMn04  =  0.000566  g.  NH3. 
Examples  of  calculations. 

It  was  found  in  one  experiment  that  the  oxides  of  nitrogen  had 
neutralized  a  quantity  of  the  alkali  in  the  two  vessels  correspond- 
ing to  0.159  g.  NH3,  reckoning  equivalents  in  nitrogen  contents. 

HNO3       HNO2       NH3 
1  c.c.  N  alkali  neutralized  =  -  =  -  =    -        =0.017g. 

NH8. 


154  AMERICAN  SULPHURIC  ACID  PRACTICE 

The  permanganate  in  estimation  (3)  was  titrated  with  N/10 
oxalic  acid.  It  was  found  that  3.5  c.c.  of  N/10KMnO4  had  been 
used  up.  This  corresponds  with  0.0035  g.  NO,  and  this  is 
equivalent  to  0.002  g.  NH3. 

After  the  converter  and  the  cooler,  all  the  unconverted  NH3 
will  have  been  removed  and  the  oxides  of  nitrogen  are  then  totally 
absorbed  in  the  absorption  bottles.  Now  in  the  estimation 
of  the  ratio  of  NH3  to  air  in  the  gas  entering  the  converter,  we 
have  determined  the  weight  of  NH3  associated  with  a  given 
volume  of  air  (the  latter  being  simply  equal  to  the  volume  of 
the  water  run  out  of  the  aspirator  bottle).  If  there  were  no 
change  of  volume  of  the  air  after  the  converter,  we  should  be 
able  to  make  a  direct  comparison  of  the  weight  of  the  oxides  of 
nitrogen,  corresponding  with  1.5  litres  aspirated  (these  oxides 
being  calculated  as  NH3)  with  the  weight  of  NH3  associated 
with  the  same  volume  (1.5  litres)  of  air  in  the  mixture  of  air  and 
NH3  entering  the  converter. 

The  aspirated  volume  after  the  converter,  however,  does  not 
represent  the  volume  of  air  which  was  associated  with  the 
ammonia  corresponding  to  the  oxides  of  nitrogen  collected,  be- 
cause a  portion  of  this  air  has  been  used  up  in  the  oxidation. 
This  consumed  oxygen  consists  of  two  parts: 

1.  A  portion  used  in  burning  the  NH3  to  NO  in  the  converter. 

2.  A  further  portion  used  in  oxidizing  the  NO  to  higher  oxides, 
which  are  then  absorbed. 

The  first  portion  is  the  same  in  all  cases,  and  is  calculated  as 
follows : 

4NH3  +  502  =  4NO  +  6H2O 
25  volumes  of  air  become  20  volumes  of  N2: 
i.e.,  the  contraction  of  the  air  volume  is  here 

(25~2°)1*22'4  =  1.647  litres  per  g.  NH3  burnt. 

(Since  the  NH3  is  completely  absorbed  from  the  gas  in  the 
aspirator,  before  the  converter,  and  the  oxides  of  nitrogen  from 
the  gas  in  the  aspirator  after  the  converter,  it  is  only  necessary 
to  consider  the  volumes  of  air.) 

The  further  contraction,  due  to  secondary  oxidation,  will 
depend  upon  the  particular  higher  oxide  of  nitrogen  produced. 
Of  these,  only  two,  namely,  N203  and  N2O4,  can  possibly  be 
produced  by  the  oxidation  of  NO  by  atmospheric  oxygen,  and 


INTRODUCTION  OF  NITRE  155 

it  is  therefore,  necessary  to  calculate  the  contractions  for  these 
two  cases  only. 

(a)  4NH3  becomes  4NO  +  O2  =  2N2O3 
that  5  volumes  air  becomes  4  volumes  N2: 

that  is,  there  is  a  contraction  of  1  volume,  i.e., 

22  4 

'    7  litres  =  0.329  litre  per  g.  NH3 

(b)  4NH3  becomes  4NO  +  202  =  2N2O4 
10  volumes  of  air  becomes  8  volumes  N2 
that  is,  a  contraction  of  2  volumes,  i.e., 

2  V  22  4 

/\    '    litres  =  0.658  litre  per  g.  NH3 

4    X   1 1 

The  aspirated  volume,  1.5  litres,  must  therefore  be  increased  in 
the  ratios: 

(a)  (Weight  of  oxides  of  N  expressed  as  NH3)  X  (1.647  + 
0.329)  :  1,  when  these  oxides  are  absorbed  as  N2O3; 

(b)  (Weight  of  oxides  of  N  expressed  as  NH3)  X  (1.647  + 
0.658)  :  1,  when  these  oxides  are  absorbed  as  N2(>4. 

The  volume  of  air  so  corrected  is  then  directly  comparable 
with  the  volume  of  air  associated  with  the  ammonia  in  the  aspira- 
tion before  the  converter,  and  if  equal  volumes  are  compared, 
the  weights  of  NH3  in  each  (that  after  the  converter  being 
calculated  from  the  titrations,  as  described)  will  give  an  imme- 
diate figure  for  the  efficiency : 

wt.  NH3  after  conversion  (as  oxides) 

wt.  NH3  before  conversion  =  effic.ency, 

the  weights  being  referred  to  equal  volumes,  as  described. 
& 

AIR  VOLUME  CORRECTION 

In  the  experiment  described  above,  the  weights  of  NH3 
corresponding  with  the  oxides  of  nitrogen  collected  in  the  alkaline 
peroxide  and  permanganate,  respectively,  were  0.159  g.  and 
0.002  g.  Since  in  a  good  experiment  the  permanganate 
figure  should  always  be  very  small,  it  is  only  necessary  to  use  the 
first  figure,  namely,  0.159  g.  in  correcting  the  air  figure. 
This  correction  will  be  as  follows : 

(a)  Gas  assumed  to  be  absorbed  as  N2O3: 

corrected  volume  of  air  =  1.5  +  0.159  X  (1.647  +  0.329)  litres 
=  1.5  +  0.314  =  1.814  litres. 


156  AMERICAN  SULPHURIC  ACID  PRACTICE 

Now  in  the  aspiration  before  the  converter,  it  was  found  that 
0.1  g.  NH3  was  contained  in  1.13  litres. 

XTTT      •        f  0*4124  U    r  !'814      X    0.1 

.   .  NH3  in  1.814  litres  before  conversion  = :— r^ —  -  = 

I.lo 

0.1605  g. 
Oxidized   NH3  after  conversion  =  0.159  +  0.002  =  0.161   g. 

/.Efficiency  =     '1fin,  X  100  =  100.1  percent, 
u.i  ouo 

(b)  Gas  assumed  to  be  absorbed  as  N2O4: 
corrected  volume  of  air  =  1.5  -f  0.159  X  (1.647  +  0.658)  litres 
=  1.867  litres. 

NH3  in  1.867  litres  air  before  conversion  =  — — r-r^ — -  = 

I.lo 

0.1650  g. 

. " .  Efficiency  =  — — n  1A, =  97.6  per  cent. 

u.loo 

The  difference  between  the  two  values  is  thus  seen  to  be  only 
about  2.5  per  cent,  which  is  within  the  limits  of  experimental 
error.  The  true  value  lies  between  the  two,  and  nearer  the  N2O3 
figure,  since  experiments  have  shown  that  about  four-fifths  of 
the  oxides  are  absorbed  as  N203  when  no  oxidizing  agent  is 
present  in  the  liquid,  and  this  ratio,  therefore,  represents  the 
composition  of  the  gas  before  absorption. 

To  the  amounts  of  oxides  of  nitrogen  collected  in  the  absorption 
bottles  must  be  added  that  present  in  the  condensed  water 
separated  from  the  cooler.  The  analysis  of  this  condensate  is  of 
value  in  estimating  the  unconverted  ammonia,  all  of  which 
separates  in  the  condensed  water  in  the  form  of  nitrite  and  nitrate. 
The  condensed  water  is  collected  throughout  the  whole  experi- 
ment and  its  volume  measured. 

An  aliquot  part  is  titrated  with  N  alkali  and  litmus  for  acidity, 
and  the  acidity  of  the  total  expressed  as  NH3  (1  c.c.  N/NaOH  = 
0.017  g.  NH3).  Another  aliquot  part  is  distilled  with  NaOH  and 
the  ammonia  collected  in  a  measured  volume  of  N/H2SO4.  This 
ammonia  was  combined  with  an  equivalent  amount  of  acid,  and 
its  value  must  therefore  be  added  to  that  found  in  the  previous 
titration,  to  obtain  the  total  OXIDIZED  NH3  in  the  condensed 
water.  This  is  divided  by  the  total  weight  of  NH3  passed 
through  the  converter  during  the  run,  and  the  result,  multiplied 
by  100,  gives  the  term  which  must  be  added  to  the  efficiency 


INTRODUCTION  OF  NITRE  157 

calculated  from  the  absorption  bottles,  to  give  the  true  efficiency. 
In  the  experiment  described  the  values  were: 

Unoxidized  NH3  =  0.3  per  cent 
Oxidized  NH3  =  0.1  per  cent 

.'.  Total  efficiency  =  100.1  +  0.4  =  100.5  or  97.6  +  0.4  = 
98.0 

If  the  proportion  of  air  and  ammonia  entering  the  converter  is 
such  as  to  form  NO,  this  could  not  be  absorbed  in  the  alkaline 
peroxide,  and  in  this  case  it  is  necessary  to  add  a  measured  volume 
of  oxygen  slowly  to  the  gases  aspirated  from  the  converter.  This 
is  done  by  connecting  a  graduated  gas-holder  containing  oxygen 
to  a  T-piece  on  the  connection  of  the  first  bottle,  the  rate  of 
addition  of  oxygen  being  controlled  by  passing  it  through  a  small 
wash-bottle  containing  water.  About  300  c.c.  of  oxygen  are 
added  during  the  whole  run  of  90  min.  This  volume  (300 
c.c.)  is  subtracted  from  the  volume  of  water  collected  and  the 
usual  correction  for  contraction  applied  to  the  remaining  volume : 

1,500  c.c.  -  300  c.c.  =  1,200  c.c.  =  1.2  litres. 

GENERAL  REMARKS 

In  the  estimation  of  the  ammonia,  the  balancing  water  column 
in  the  Winchester  bottle  should  be  such  that  the  gas  pressure 
before  the  converter  is  just  sufficient  to  bubble  through  the  water. 
As  soon  as  the  aspirator  is  started  bubbles  will  pass,  and  the  rate 
should  be  adjusted  so  that  the  color  of  the  indicator  changes  in 
about  10  min.  When  indications  of  a  color  change  appear,  the 
rate  of  aspiration  should  be  reduced  so  that  about  one  bubble 
per  second  passes,  and  the  absorption  bottle  should  be  shaken. 
The  connecting  tubes  and  the  upper  part  of  the  tube  in  the  wash- 
bottle  should,  of  course,  be  dry. 

The  alkaline  peroxide  bottles  should  be  carefully  fitted  together, 
so  that  on  opening  the  tap  connecting  with  the  outlet  from  the 
converter,  on  bubbles  (or  at  most  one  or  two)  pass  before  the 
aspirator  is  started.  The  rate  of  aspiraton  must  be  slow,  as 
stated.  If  white  fumes  appear  in  the  second  bottle,  or  the  per- 
manganate is  discolored,  or  deposits  much  MnO2,  the  experi- 
ment will  usually  be  found  to  give  an  incorrect  result. 

If  oxygen  is  added  it  should  be  let  in  slowly,  as  stated,  in  order 
to  insure  that  the  whole  of  it  passes  through  the  aspirator  bottles, 
and  not  backwards  into  the  converter  main. 


158  AMERICAN  SULPHURIC  ACID  PRACTICE 

To  insure  that  the  pressures  are  equalized  in  the  aspirator 
bottles,  these  may  be  provided  with  gauges,  consisting  of  U-tubes 
containing  water. 

Hydrogen  peroxide  solution  is  usually  acid,  and  allowance 
must  be  made  for  this  in  the  titrations. 

(b)  Determination  Without  the  Use  of  Cooler. — If  the  hot  gases 
from  the  converter  are  utilized  without  previous  cooling  it  has 
been  found  that  a  short  length  of  aluminum  tubing,  inserted  as  a 
T-tube  in  the  main  from  the  converter,  is  generally  sufficient  in 
itself  to  cool  the  aliquot  part  of  the  gases  which  are  slowly  passing 
through  it  to  the  absorption  system.  It  has  been  usual  to  neglect 
the  small  portion  of  unoxidized  ammonia  in  this  case.  As  alter- 
natives the  following  suggestions  are  based  upon  information 
from  those  who  have  had  occasion  to  carry  out  control  tests  on 
hot  converter  gases: 

1.  The  converter  gas  is  drawn  slowly  through  a  capillary  tube 
to  an  absorption  system  similar  to  that  described  above. 

2.  The  first  absorption  bottle  contains  N/10  alkali  without 
peroxide.     This,    according  to  Fox  (Journal  of  Industrial  and 
Engineering  Chemistry,  August,  1917),  retains  all  the  unoxidized 
ammonia  coming  over,  the  amount  of  which  is  estimated  after 
the  titration  by  treatment  with  caustic  soda  and  sodium  hypo- 
bromite,  when  nitrogen  is  liberated  and  is  measured  (cf.,  Tread- 
well  and  Hall,  Quantitative  Analysis,  p.  622).     A  correction  must 
be  applied  to  this  volume  of  nitrogen,  since  the  reaction  is  not 
quite  complete  (cf.,  Fox). 

3.  The  second  absorption  bottle  contains  the  same  solution  as 
the  first  bottle  in  the  method  described  above. 

4.  The  permanganate  tube  is  retained  unchanged. 


CHAPTER   XIII 
DRAFT 

Early  chamber  plants  depended  upon  natural  draft  for  the 
movement  of  gases  through  the  apparatus,  but  all  modern  plants 
use  fans.  In  this  way  larger  volumes  can  be  moved  and  the  con- 
trol is  much  more  positive. 

Fans  are  of  two  classes,  viz.,  iron  fans  which  are  used  at  some 
point  preceding  the  Glover  Tower,  and  lead  fans,  used  at  some 
point  following  the  Glover  Tower.  Sometimes  both  kinds  are 
used  in  the  same  system.  It  must  be  understood  that  if  a  fan 
is  placed  between  the  sulphur  burners  or  roasters  and  the  Glover 
Tower,  high  temperature,  dry  gases  are  to  be  handled  and  iron 
is  the  only  suitable  material  for  the  service.  If  the  fan  is  placed 
at  any  point  beyond  the  Glover  Tower,  comparatively  low  tem- 
perature gases  laden  with  sulphuric  acid  mist  are  to  be  propelled. 
For  this  service  lead,  usually  stiffened  by  alloying  with  antimony, 
is  the  most  suitable  material.  Iron  of  course  would  be  quickly 
destroyed  by  the  acid.  Lead  fans  are  more  often  used  than  iron 
though  the  latter  certainly  deserve  much  consideration  as  they 
have  many  advantages. 

The  arrangement  most  common  for  units  of  moderate  size  is 
to  use  a  single  lead  fan  between  the  Glover  Tower  and  the  first 
chamber.  Very  often  a  second  lead,  fan  is  used  between  the  last 
chamber  and  the  Gay  Lussacs.  A  less  frequent  plan  is  to  use  a 
single  iron  fan  just  in  front  of  the  Glover  or  an  iron  fan,  with  a 
lead  fan  between  the  last  chamber  and  the  Gay  Lussacs.  Any  of 
these  arrangements  of  suitable  size  and  with  the  other  features 
of  the  plant  in  conformity  may  give  good  results.  It  is  well  to 
consider  that  the  fans  are  of  very  vital  importance  to  continuous 
operation  and  that  they  have  to  be  repaired  and  parts  replaced  at 
times.  If  there  are  two  fans  in  a  system  with  proper  by-passes 
one  of  them  may  be  cut  out  and  worked  on  without  causing  a 
shutdown.  To  be  sure  a  diminished  production  will  probably 
result  but  that  is  not  nearly  so  serious  as  cooling  off  furnaces  and 
discontinuing  the  acid  making  process.  A  further  important 
advantage  of  having  a  fan  at  each  end  of  the  system  is  that  repairs 

159 


160  AMERICAN  SULPHURIC  ACID  PRACTICE 

may  be  made  on  the  chambers  more  readily  by  producing  a  slight 
inward  suction  by  varying  the  fan  speeds.  This  is  appreciated 
after  chambers  become  several  years  old. 

Iron  fans  suitable  for  this  work  are  similar  in  general  design 
to  those  used  for  many  other  purposes,  such  as  ventilation  of 
mines,  buildings,  etc.  They  must  of  course  be  quite  tight,  able 
to  stand  temperatures  up  to  1,000°F.  and  be  of  simple  construc- 
tion to  avoid  catching  dust.  The  housing  should  be  of  cast  iron 
as  plate  housings  will  warp  badly  in  the  heat  encountered.  The 
shaft  will  be  course  be  very  hot  for  some  distance  outside  the 
housing  and  so  the  bearings  must  be  water  cooled.  The  rotor 
can  be  of  cast  iron  or  of  steel  plate  with  a  cast  hub  spider.  It 
may  be  overhung  or  may  have  a  bearing  on  each  side  of  the  hous- 
ing. The  former  method  is  perhaps  more  convenient  as  the 
inlet  flue  is  not  complicated  by  having  a  shaft  and  bearing  on  that 
side. 

The  speed  of  iron  fans  should  be  from  500  to  1,000  r.p.m.  in 
order  that  they  may  blow  the  dust  out  and  keep  themselves 
clean.  It  must  also  be  considered  that  due  to  its  high  tempera- 
ture the  volume  of  the  gas  is  more  than  twice  what  it  is  after 
it  passes  through  the  Glover  Tower.  Consequently,  the  range 
of  speed  specified  is  advisable  in  order  to  move  the  gas  with  a  fan 
not  unduly  large. 

Several  manufacturers  in  this  country  have  stock  designs 
which  with  slight  modifications  are  entirely  satisfactory  for  acid 
plant  service.  These  fans  are  very  much  less  expensive  than  the 
lead  fans  and  over  a  period  of  years  require  less  repairs.  Why 
they  are  not  used  more  is  hard  to  understand.  ' 

Lead  fans  are  in  general  much  like  the  iron  fans  in  design. 
It  is  necessary  on  account  of  the  low  strength  of  lead  to  make  the 
metal  much  thicker  than  corresponding  parts  of  iron.  The 
shaft  which  carries  the  rotor  is  necessarily  of  steel,  but  it  is 
entirely  covered  by  lead  until  it  leaves  the  housing.  Usually 
the  lead  of  the  spider  is  poured  around  a  cast  iron  hub  which 
latter  is  keyed  to  the  shaft.  This  is  a  detail  which  has  given 
trouble  in  many  fans,  but  if  the  cast  iron  hub  is  generous  in 
size  and  made  with  dovetail  grooves  so  that  the  lead  can  take 
hold  of  it  well,  no  slipping  or  working  loose  will  occur. 

There  are  several  lead  fans  specially  designed  for  acid  plant 
work  on  the  market,  and  most  of  the  manufacturers  of  blowers, 
will  alter  their  designs  of  iron  fans  and  make  them  of  lead  if 


DRAFT 


161 


desired.     Two  widely  used  specially  designed  fans  are  the  Pratt 
and  the  Heinz-Skinner. 

The  Pratt  fan,  shown  in  Fig.  52,  is  made  with  both  bearings 
on  one  side,  i.e.,  with  rotor  overhung.  The  gas  enters  on  one  side 
only.  The  housing  is  of  cast  hard  lead  made  in  two  pieces  and 
is  self-supporting.  It  is  so  arranged  that  the  top  casting  can  be 
lifted  off  to  allow  removal  of  the  rotor.  This  is  a  well-designed 
fan  with  the  details  perfected  over  a  period  of  several  years. 
This  fan  is  designed  to  run  at  rather  high  speeds  up  to  800  or  900 
r.p.m.  It  is  therefore  small  comparatively  and  uses  more  power 
than  the  large  low  speed  fan. 


FIG.  52. 

The  Heinz-Skinner,  Fig.  53,  has  several  novel  features  though 
the  principle  upon  which  it  works  is  the  usual  one.  This  fan  has 
its  shaft  extending  clear  through  the  housing  with  a  bearing  on 
each  side.  The  inlet  pipe  branches  just  before  it  reaches  the  fan 
and  goes  to  an  inlet  on  each  side  of  the  rotor.  The  housing  is  in 
two  parts  with  a  horizontal  joint  at  the  level  of  the  shaft.  The 
joint  itself  is  a  lute  made  tight  by  an  acid  seal.  The  upper  part 
of  the  housing  can  be  lifted  off  to  change  or  work  at  the  runner. 
This  fan  both  as  to  housing  and  runner  is  largely  built  up  by 
burning  together  rolled  hard  lead  plates.  It  is  entirely  of  hard 

lead  excepting,  of  course,  the  shaft.     This  fan  is  also  very  well 
11 


162 


AMERICAN  SULPHURIC  ACID  PRACTICE 


designed  and  if  properly  handled  gives  good  service.     It  runs  at 
speeds  up  to  500  or  600  r.p.m. 

The  Wedge  fan  which  has  been  used  in  several  large  acid 
units  built  of  late  years  is  something  of  a  departure  from  the 
above  types  in  the  matter  of  size  and  speed.  This  fan  so  far  as 
I  know  is  not  made  regularly  by  any  manufacturer.  The  fans 


-Heavily 
ffibb&t 


FIG.  53. 

so  far  made  have  all  had  runners  8  ft.  in  diameter  and  4  ft.  wide. 
They  run  at  speeds  not  over  200  r.p.m.  They  are  enormously 
heavy  and  costly  but  they  run  with  surprisingly  little  power  and 
give  very  little  trouble.  Some  of  them  have  been  in  practically 
continuous  use  for  more  than  4  years  without  being  opened. 
The  housing  of  this  fan  is  built  up  of  ordinary  sheet  lead  (15-lb.) 
supported  by  angle  iron  framework.  There  is  a  gas  inlet  on  one 


DRAFT  163 

side  only.  The  shaft  runs  in  a  bearing  on  each  side  of  the 
housing.  One  fan  of  this  size  will  provide  draft  for  a  properly 
designed  plant  to  make  125  to  150  tons  of  60°  acid  per  day.  It 
consumes  only  12  to  15  H.P.  at  200  r.p.m. 

These  fans  are  mentioned  specifically  not  so  much  because 
they  are  more  satisfactory  than  many  others,  but  because  they 
represent  types  and  because  they  are  specially  designed  for  acid 
plant  service. 

FLUES 

As  the  parts  of  the  chamber  system  are  enclosed  in  sheet  lead 
considerable  areas  of  which  are  unsupported,  it  is  essential  that 
flues,  tower  packing,  etc.,  be  so  proportioned  that  no  very  great 
resistances  shall  be  offered  to  the  passage  of  the  gas.  Of  course, 
the  towers  can  stand  somewhat  higher  differences  between 
internal  and  atmospheric  pressures,  than  can  the  chambers, 
because  they  are  of  heavier  lead  and  the  internal  masonry  lends 
them  stability. 

It  is  well  to  so  design  the  plant  that  pressures  corresponding  to 
1-in.  of  water  shall  not  be  exceeded  in  any  tower  and  0.75  in.  as 
a  maximum  for  any  chamber.  Of  course,  higher  pressures  will 
be  found  in  many  plants  and  it  should  not  be  inferred  that  they 
are  particularly  dangerous;  however,  the  fact  is  that  lead  at  a 
temperature  of  200°F.  is  not  very  stiff  and  in  the  course  of  some 
years  high  pressures  cause  distortions  which  make  trouble. 

Calculations  for  flue  areas  must  be  made  for  individual  cases, 
but  the  following  statements  will  give  an  idea  of  proper  areas 
which  should  be  provided  in  a  simple  one-fan  system.  If  the 
gas  entering  the  acid  system  contains  an  average  of  7  per  cent  SO2 
by  volume,  it  will  be  necessary  to  put  through  the  plant  about 
80,000  cu.  ft.  per  24  hours  per  ton  of  60°  acid  made,  at  0°C.  and 
760  m.m.  This  will  be  increased  somewhat  by  the  reaction 
temperature  and  decreased  as  SO2  and  O  go  to  make  liquid  H2SO4. 
In  the  early  parts  of  the  system  for  example,  the  gas  temperature 
may  be  100°C.  which  would  make  80,000  cu.  ft.  at  0°  =  109,000 
cu.  ft.  =  1.26  cu.  ft.  per  sec.  If  we  wish  the  gas  velocity  to  be 
10  ft.  per  sec.  our  flue  area  in  this  part  of  the  system  would  be 
.126  sq.  ft.  per  ton  of  60°  acid  made.  For  a  100  ton  unit  the 
flue  area  should  then  be  12.6  sq.  ft.  which  is  almost  exactly  that 
of  a  48-in.  diameter  flue. 

In  the  back  part  of  the  system  where  the  gas  temperature  is 


164  AMERICAN  SULPHURIC  ACID  PRACTICE 

perhaps  45°C.,  the  volume  will  have  decreased  on  this  account  to 
about  86,000  cu.  ft.  The  reaction  and  condensation  of  SO2  and  O 
to  liquid  acid  will  have  removed  about  10  per  cent  by  volume  or 
8,600  cu.  ft.  so  that  the  volume  of  gas  per  ton  of  acid  will  be 
about  77,400  cu.  ft.  per  24  hours  =  .9  cu.  ft.  per  sec.  and  the 
necessary  flue  area  will  be  9.0  sq.  ft.  which  is  the  area  of  a  pipe 
about  41  in.  diameter. 

If  several  small  flues  are  to  be  used  instead  of  one  large  one, 
or  if  there  are  many  bends  or  very  long  distances  between  parts 
of  the  apparatus  which  the  flues  connect,  some  allowances  to 
compensate  for  increased  friction  should  be  made.  The  basis 
of  10  ft.  per  sec.  is  a  safe  one  however  for  the  flue  connections 
found  in  most  plants. 


FIG.  54. 

For  tower  packing,  no  very  definite  figure  can  be  given  as  a 
minimum  of  necessary  open  area,  experience  and  data  on  different 
types  of  packing  are  necessary.  It  is  also  necessary  to  consider 
the  length  of  the  column  of  packing  through  which  the  gas  must 
pass.  It  is  well  in  a  Glover  tower  having  a  packed  column 
25  or  30  ft.  high  to  provide  a  gross  horizontal  packed  area  of  not 
under  2  sq.  ft.  per  ton  of  60°  acid  made.  For  Gay  Lussacs, 
where  combined  packed  heights  amount  to  75  ft.  or  more,  2  to 
2.5  sq.  ft.  per  ton  of  60°  acid  made  should  be  provided.  Con- 
siderable divergences  from  these  specimen  figures  may  be  made 
with  entire  propriety  by  using  fans  at  various  points  of  the 
system. 

Circular  lead  flues  are  to  be  preferred  to  rectangular  sections. 


DRAFT  165 

They  are  stronger  from  the  nature  of  their  section  and  are 
simpler  to  support.  Sharp  angles  are  to  be  avoided,  in  general, 
in  lead  construction.  Circular  flues  are  best  made  of  10-lb.  lead. 
The  supports  are  flat  or  edge  bands  of  iron  as  shown  in  Fig.  54. 
The  edge  bands  are  slightly  more  expensive  to  apply  but  are 
distinctly  better  in  the  long  run.  Bands  should  be  frequent  as 
in  the  later  years  of  the  life  of  a  plant  insufficient  support  of 
flues  causes  much  trouble. 


CHAPTER  XIV 
TESTING 

The  control  tests  made  about  an  acid  plant  are  largely  per- 
formed by  men  who  have  little  knowledge  of  the  refinements  of 
chemical  and  physical  measurements  and  consequently  no  high 
degree  of  accuracy  is  customary.  Nor  is  a  high  degree  of  accu- 
racy necessary.  The  tests  and  instruments  to  be  described  are 
intended  only  to  represent  such  work.  They  are  for  the  operator 
rather  than  for  the  chemist. 

THERMOMETERS  AND  PYROMETERS 

It  is  desirable  in  many  parts  of  the  plant  to  know  the  tem- 
peratures of  the  gases  and  acids  involved  in  the  process  and  for 
obtaining  these,  thermometers  and  pyrometers  are  used.  Every- 
one is  familiar  with  thermometers  and  little  need  be  said  concern- 
ing them.  In  the  United  States  the  Fahrenheit  scale  is  almost 
universally  used.  For  taking  acid  temperatures,  straight  stem 
thermometers  with  inclosed  paper  scales  reading  up  to  220°F. 
are  best.  They  are  less  expensive  and  more  easily  read  than  the 
engraved  instruments.  It  is  well  to  have  a  few  thermometers 
reading  up  to  400°  for  testing  the  acid  issuing  from  the  Glover 
tower.  Chamber  thermometers  having  stems  bent  at  45°  or 
90°  from  the  graduated  portion  are  regularly  made  by  the 
manufacturers  of  chemical  apparatus.  The  stems  are  inserted 
into  the  chambers  through  rubber  stoppers.  In  reading  a 
thermometer  it  is  important  that  a  line  from  the  eye  to  the  end 
of  the  mercury  column  be  at  a  right  angle  to  the  latter. 

For  ascertaining  high  temperatures  such  as  those  of  the  gases 
entering  the  Glover  Tower,  the  pyrometer  is  used.  When 
certain  dissimilar  metals  or  alloys  are  placed  in  contact  with  each 
other  and  heated,  an  electric  current  is  set  up  which  can  be 
measured  by  a  galvanometer  and  the  corresponding  degree  of 
heat  shown  by  a  needle  on  a  graduated  scale.  For  the  purposes 
of  the  chamber-acid  plant  what  are  known  as  base  metal  couples 
for  insertion  into  the  flue  are  most  suitable.  This  form  of 
couple,  shown  in  -Fig.  55  consists  of  a  pipe  or  tube  of  one 
metal  and  a  rod  of  a  different  metal  inside  it  and  insulated  from 

166 


TESTING 


167 


it  except  at  one  end  where  the  tube  and  the  rod  are  welded 
together.  This  welded  end  constitutes  the  couple  and  is  inserted 
into  the  gas  whose  temperature  is  desired.  Couples  made  of 
platinum,  and  platinum  alloyed  with  rhodium  or  indium,  are 


FIG.  55. 

excellent  but  far  more  expensive.  The  only  precautions  neces- 
sary to  be  observed  in  using  pyrometers  are  to  have  all  the  wire 
connections  clean  and  tight  and  to  keep  the  couple  reasonably 
free  from  dust. 

Several  couples  may  lead  through  switches  to  one  galvano- 
meter. Temperatures  exceeding  1,200°F.  are  not  often  encoun- 
tered in  flues  so  that  an  instrument  graduated  to  1,500°  or 
1,600°F.  is  suitable. 

HYDROMETERS 

The  hydrometer  is  an  instrument  used  for  showing  the  concen- 
tration of  sulphuric  acid.  It  is  made  of  glass  and  consists  of  a 
cylindrical  float  weighted  at  its  lower  end  and  with  mercury,  or 
shot,  and  surmounted  by  a  thin  stem 
containing  a  graduated  paper  scale. 

The  acid  to  be  tested  is  placed  in  a  tall 
jar  and  the  hydrometer  allowed  to  sink  in 
it  until  it  comes  to  rest.  On  account  of 
surface  tension,  the  acid  will  curve  up  A— 
against  the  stem  as  shown  in  Fig.  56. 
The  reading  should  be  taken  across  the 
surface  of  the  acid  on  line  AA,  not  at  the 
top  of  the  curve  line,  BB. 

The  hydrometer  universally  used  in 
chamber-acid  plants  in  this  country  is 
called  the  American  Beaume*.  This  is  an 
arbitrary  scale  originally  devised  by 
making  up  a  solution  of  pure  salt,  NaCl,  15  parts  and  pure  water 
85  parts  by  weight;  immersing  a  hydrometer  in  it  and  calling  the 
mark  15°.  The  point  to  which  the  hydrometer  sunk  in  pure 
water  was  called  0°.  The  distance  between  these  marks  was 
divided  into  15  equal  parts,  thus  establishing  the  degree  Beaume. 
After  many  years  of  disagreement  over  the  exact  details  of 


-40 


-30 


Correct  Reading 
AAno+BB 


FIG.  56. 


168  AMERICAN  SULPHURIC  ACID  PRACTICE 

obtaining  the  degree  and  as  to  its  relation  to  specific  gravity,  the 
U.  S.  Bureau  of  Standards  adopted  as  the  official  American 
standard  the  relation  expressed  thus: 

Degrees  Beaum£  =  145  —  ~  —  ~- 

bp.  (jr. 

In  England  Twaddles  Hydrometer  is  most  used.  It  is  based 
strictly  upon  a  specific  gravity  relation.  Specific  gravity  1.0  = 
0°  Tw  —  and  each  succeeding  degree  represents  an  increase  of 
.005  in  specific  gravity,  e.g.,  5°  Tw  =  1.025  sp.  g.  This  scale  is 
very  little  used  in  the  United  States. 

Standard  hydrometers  are  made  for  use  in  liquids  at  60°F. 
If  the  liquid  is  warmer  than  60°F.  the  hydrometer  will  read  low 
and  vice  versa,  if  the  liquid  is  colder  than  60°F.  Where  sulphuric 
acid  is  said  to  be  so  many  degrees  Beaume  it  is  understood  that 
the  statement  refers  to  the  hydrometer  reading  at  60°F.  When 
it  is  desired  to  determine  what  the  hydrometer  would  read  at 
60°F.  in  acid  which  is  warmer  or  cooler  than  60°F.,  the  hydro- 
meter is  read  at  the  existing  temperature  and  the  temperature  of 
the  acid  taken  with  a  thermometer.  The  hydrometer  reading  is 
then  corrected,  increased  if  the  acid  is  warmer  than  60°  and 
decreased  if  colder. 

If  the  acid  is  near  40°Be.  .031°Be.  for  each  1°F.  above  or  below  60° 
If  the  acid  is  near  50°Be.  .028°Be.  for  each  1°F.  above  or  below  60° 
If  the  acid  is  near  60°Be.  .026°Be\  for  each  1°F.  above  or  below  60° 

The  Manufacturing  Chemists  Association  of  the 
United  States  has  adopted  the  tables  of  Ferguson 
and  Talb.ot  as  a  standard  for  the  relationships  be- 
tween specific  gravity,  degrees  Beaume,  degrees 
Twaddel  and  per  cent  H2SO4.  This  table  is  very 
generally  used  in  the  United  States.  It  can  be  found 
in  Chapter  XXIII,  Table  1. 

Hydrometers   most  useful  in  the  chamber  acid 
plant  are  the  long  12-in.  form  with  a  range  from  50°  to 
70°  graduated  to  tenths  of  each  degree  and  the  short 
chamber  5-in.  hydrometer  with  a  range  of  40  to  60° 
graduated  in  degrees.     The  former  is  used  for  testing 
the  tower  acids  and  the  latter  for  the  chamber  drips. 
Hydrometer  jars  for  control  testing  are  made  of  glass  or  lead 
in  the  form  shown  in  Fig.  57.    The  acid  enters  the  main  jar  from 
the  bottom  and  assures  the  jar  being  full  of  the  current  flow. 


f) 

C.  ^jT  ^> 
~ 


TESTING 


GAS  TESTING 


169 


The  constituents  of  the  gases  regularly  determined  are  S02  and 
oxygen.  The  Orsat  apparatus  is  very  generally  used  for  deter- 
mining both  of  these  in  the  gases  entering  the  system.  In  the 
latter  parts  of  the  plant  where  the  S02  percentage  of  the  gas  is 
very  low  the  Orsat  is  not  suitable. 

The  Orsat  apparatus  consists  essentially  of  a  measuring  burette 
graduated  to  100  c.c.,  two  absorption  pipettes,  connecting  capil- 
lary tubes  with  stop  cocks,  and  a  levelling  bottle.  One  pipette 
is  charged  with  30°Be*.  caustic  soda  solution  which  absorbs  SO2 
and  the  other  with  a  solution  of  pyrogallic  acid  in  caustic  soda, 
which  absorbs  oxygen.  This  is  shown  in  Fig.  58.  To  operate 
the  Orsat  apparatus  the  end  of  the  glass  capillary  is  connected 


FIG.  58. 


with  the  vessel  containing  the  gas  to  be  analyzed  by  a  rubber 
tube.  Three-way  cock  E  is  turned  to  open  from  burette  B  to 
waste.  Bottle  A  is  raised  to  expel  air  from  B  and  fill  B  with 
water.  Cock  E  is  turned  so  that  B  communicates  with  V, 
bottle  A  is  lowered  and  the  burette  drawn  full  of  gas.  In  order 
to  be  sure  of  a  fresh  complete  gas  sample  the  cock  is  turned  to  the 
waste  position  and  the  gas  in  burette  expelled.  A  second  sample 
is  drawn  and  the  bottle  manipulated  so  that  the  water  in  the 
burette  stands  at  O  when  bottle  A  is  held  so  that  water  in  A  and 
B  are  level,  with  cock  E  closed.  Cock  to  C  is  now  opened,  bottle 
is  raised  and  gas  all  forced  into  C.  The  gas  is  drawn  back  and 
forth  between  B  and  C  five  times,  then  with  level  of  liquor  in  C 
at  original  mark  and  cock  closed  a  reading  is  taken  in  B  with 
water  in  A  and  B  held  level.  This  reading  is  noted.  The  gas  is 
again  drawn  back  and  forth  between  B  and  C  twice  and  the 


170  AMERICAN  SULPHURIC  ACID  PRACTICE 

reading  in  B  taken  as  before.  If  the  two  readings  check,  all  the 
SO2  is  considered  to  have  been  absorbed  in  C.  If  the  second 
reading  is  greater  than  the  first  the  gas  is  sent  into  C  again  and 
until  two  readings  do  check.  The  final  reading  in  cubic  centi- 
meters represents  the  per  cent  S02  by  volume.  Next  the  gas  is 
manipulated  into  D  and  the  same  procedure  gone  through  as 
with  C.  The  difference  between  the  reading  obtained  from 
absorption  in  C  and  that  in  D  indicates  the  per  cent  of  oxygen  by 
volume.  It  is  well  to  keep  a  thin  rubber  bulb  on  the  back  limb 
of  D  so  that  fresh  air  is  not  drawn  in  on  the  pyrogallic  acid 
solution  with  each  test,  otherwise  the  absorbing  power  of  the 
solution  is  quickly  destroyed. 

In  gases  free  from  CO 2  and  which  contain  several  per  cent  of 
S02  the  Orsat  test  will  answer  very  well  for  testing  in  connection 
with  chamber  control  work.  The  accuracy  is  perhaps  not  high, 
but  the  test  can  be  reliably  performed  by  any  reasonably  intelli- 
gent person  and  it  gives  a  good  basis  for  estimating  necessary 
changes  in  nitric  feed  and  working  the  S02  furnaces. 

The  caustic  soda  solution  used  is  made  by  dissolving  about 
300  g.  pure  caustic  soda  in  a  litre  of  water.  It  is  not  necessary 
to  have  these  proportions  exact. 

The  pyrogallic  acid  solution  is  made  by  dissolving  about  12  to 
15  g.  pyrogallic  acid  in  125-150  c.c.  of  the  above  caustic  soda 
solution.  This  amount  is  a  suitable  volume  for  charging  the 
customary  Orsat  pipette.  The  caustic  solution  can  be  made  up 
in  any  volume  desired  and  kept  indefinitely  in  a  glass-stoppered 
bottle.  The  pyrogallic  acid  solution  is  best  made  up  as  it  is 
wanted  to  charge  the  pipettes.  It  is  well  systematically  to 
change  the  solutions  once  a  week  or  at  sufficient  intervals  to 
assure  that  the  solutions  do  not  become  sluggish. 

A  direct  test  for  SO2  suitable  for  any  gas  found  in  chamber 
work  is  the  Reich  Test.  This  depends  upon  the  reaction  between 
iodine  and  S02  -  21  +  S02  +  2H2O  =  2HI  +  H2SO4,  and  upon 
the  fact  that  a  solution  of  cooked  starch  produces  a  deep  blue 
color  in  a  solution  containing  free  iodine,  and  that  the  color 
disappears  as  soon  as  all  free  iodine  has  been  reduced  to  HI. 

The  test  is  performed  in  apparatus  shown  in  Fig.  59.  Bottle 
A  is  charged  with  a  definite  weight  of  iodine  dissolved  in  KI 
solution  and  colored  with  starch.  Syphon  tube  C  is  opened  and 
the  gas  under  observation  is  drawn  through  the  iodine  solution 
until  the  color  just  disappears.  The  amount  of  water  drawn 


TESTING 


171 


from  B  is  noted  and  it  represents  the  amount  of  gas  drawn 
through  the  iodine  solution,  less  the  S02  absorbed.  Knowing  the 
amount  of  iodine  used  and  the  volume  of  gas  drawn,  the  per  cent 
SO2  by  volume  is  readily  calculated. 

As  a  rule  tests  are  made  in  a  chamber  plant  at  a  point  near  the 
Glover  tower  where  the  SO2  percentage  is  from  5  to  8,  and  at  a 
point  near  the  Gay  Lussacs  where  the  SO2  percentage  is  under 
y±Q.  For  the  former  it  is  convenient  to  use  a  Ko  normal  iodine 
solution,  i.e.,  one  which  contains  12.7  g.  iodine  per  litre.  For 


lodin 
Solution 


FIG.  59. 


each  test  10  c.c.  of  this  solution  is  used  and  a  table  is  made  up  in 
the /following  way. 

Ten  cubic  centimeters  of  ^{Q  normal  iodine  contains  .127 
g.  iodine.  According  to  the  reaction  above  this  amount  of  iodine 
will  react  with  .032  g.  S02. 

21  :  S02  =  10  c.c.  N/10  I  :  wt,  SO2 
2  X  127  :  64  =  .127  g.  :  .032  g. 

.032  g.  S02  =  11.184  c.c.  S02  at  0°C.  and  760  m.m. 

The  total  volume  of  gas  drawn  into  the  iodine  solution  in  any  test 
is  then  the  amount  of  water  syphoned  from  the  bottle  B  plus 


172  AMERICAN  SULPHURIC  ACID  PRACTICE 

11.184  c.c.  which  is  the  volume  of  SO2  absorbed.     Therefore 

per  cent.  SO2  = 11'1.84        +11.184 

c.c.  water 

and  c.c.  water  =  - —          —57^ 11.184 

per  cent.  SO2 

From  this  equation  Table  6  is  constructed. 

In  the  rear  of  the  system  a  1/500  normal  iodine  solution  is 
suitable.  This  contains  .254  g.  per  litre.  Table  7  is  con- 
structed for  this  solution  in  the  same  way  as  described  for  6. 

In  using  the  Reich  test,  at  any  point  in  the  chamber  system 
following  the  Glover  tower,  a  modification  is  necessary.  The 
nitrogen  oxids  contained  in  the  gas  mixture  render  the  test  as 
described  above  worthless  in  that  they  reoxidize  the  HI  formed 
and  prevent  decolorization  of  the  solution.  This  can  be  pre- 
vented and  the  test  made  fairly  accurate  by  adding  to  the  iodine 
solution  just  before  making  the  test,  10  or  15  c.c.  of  a  solution 
containing  100  g.  sodium  acetate  and  100  g.  acetic  acid  per 
litre. 

In  Fig.  59  bottle  A  should  be  a  12  oz.  salt  mouth  bottle  fitted 
with  a  two  hole  rubber  stopper  carrying  two  tubes.  One  of  these 
extends  to  within  a  short  distance  of  the  bottom.  Its  end  is 
drawn  down  so  that  the  opening  is  only  1  or  1J^  mm.  in  diameter 
in  order  that  the  gas  bubbles  shall  be  small.  The  second  tube 
goes  barely  through  the  stopper.  This  arrangement  is  for  all 
practical  purposes  as  good  as  the  expensive  and  elaborate  absorp- 
tion bottles  and  when  it  is  broken,  it  is  quickly  and  cheaply 
replaced.  The  syphon  bottle  B  should  be  at  least  two  or  three 
litres.  Two  graduated  cylinders,  a  500  c.c.  and  a  1000  c.c.  should 
be  provided. 

The  Jfo  normal  iodine  solution  is  made  by  dissolving  15 
or  20  c.c.  of  potassium  iodide  crystals  in  25  c.c.  of  water.  Into 
this  solution  dissolve  12.7  g.  iodine  crystals.  It  is  important 
that  the  KI  solution  be  very  concentrated  or  else  the  iodine  will 
be  slow  to  dissolve.  When  solution  is  perfect,  make  up  to  one 
litre  with  water. 

The  J^oo  normal  solution  is  made  by  making  up  20  c.c.  of  the 
Jf  0  normal  solution  to  one  litre  with  water. 

Starch  solution  is  made  by  mixing  5  or  6  g.  soluble  starch  to  a 
thin  paste  and  pouring  into  500  c.c.  of  boiling  water  and  allowing 
to  boil  for  5  min.  The  addition  of  a  few  drops  of  chloroform  or 


TESTING 

TABLE  6. — STANDARD  SO2  TABLE 
10  c.c.  N/10  Iodine.  0°C.-760  mm. 


173 


Per  cent 
SO2 

C.c.  water 

Per  cent 
SO2 

C.c.  water 

Per  cent 
S02 

C.c.  water 

.1 

11,173 

4.1 

262 

8.1 

127 

.2 

5,581 

4.2 

255 

8.2 

125 

.3 

3,717 

4.3 

249 

8.3 

124 

.4 

2,785 

4.4 

243 

8.4 

122 

.5 

2,226 

4.5 

237 

8.5 

120 

.6 

1,853 

4.6 

232 

8.6 

119 

.7 

1,587 

4.7 

227 

8.7 

117 

.8 

1,387 

4.8 

222 

8.8 

116 

.9 

1,231 

4.9 

217 

8.9 

114 

1.0 

1,107 

5.0 

212 

9.0 

113 

1.1 

1,006 

5.1 

208 

9.1 

112 

1.2 

921 

5.2 

204 

9.2 

110 

1.3 

849 

5.3 

200 

9.3 

109 

1.4 

,788 

5.4 

196 

9.4 

108 

.5 

734 

5.5 

192 

9.5 

107 

.6 

688 

5.6 

189 

9.6 

105 

.7 

647 

5.7 

185 

9.7 

104 

.8 

610 

5.8 

182 

9.8 

103 

.9 

577 

5.9 

178 

9.9 

102 

2.0 

548 

6.0 

175 

10.0 

101 

2.1 

521 

6.1 

172 

10.1 

99.5 

2.2 

497 

6.2 

169 

10.2 

98.5 

2.3 

475 

6.3 

166 

10.3 

97.4 

2.4 

455 

6.4 

164 

10.4 

96.4 

2.5 

436 

6.5 

161 

10.5 

95.3 

2.6 

419  • 

6.6 

158 

10.6 

94.3 

2.7 

403 

6.7 

156 

10.7 

93.3 

2.8 

388 

6.8 

153 

10.8 

92.3 

2.9 

374 

6.9 

151 

10.9 

91.4 

3.0 

362 

7.0 

149 

11.0 

90.5 

3.1 

350 

7.1 

146 

11.1 

89.6 

3.2 

338 

7.2 

144 

11.2 

88.7 

3.3 

328 

7.3 

142 

11.3 

87.8 

3.4 

318 

7.4 

140 

11.4 

86.9 

3.5 

308 

7.5 

138 

11.5 

86.1 

3.6 

299 

7.6 

136 

11.6 

85.2 

3.7 

291 

7.7 

134 

11.7 

84.4 

3.8 

283 

7.8 

132 

11.8 

83.6 

.3.9 

276 

7.9 

130 

11.9 

82.8 

*4.0 

268 

8.0 

129 

12.0 

82.0 

This  table  is  calculated  using  2.8611  g.  as  the  weight  of  the  litre  of  SO2. 


174 


AMERICAN  SULPHURIC  ACID  PRACTICE 


TABLE  7.— SO2  BY  REICH  TEST 
10  C.c.  N/500  Iodine 


Per  cent  SO2 

C.c.  water 

Per  cent  SO2 

C.c.  water 

.010 

2,236 

.060 

373 

.015 

1,491 

.065 

343 

.020 

1,118 

.070 

319 

.025 

894 

.075 

298 

.030 

745 

.080 

279 

.035 

639 

.085 

263 

.040 

559 

.090 

248 

.045 

497 

.095 

235 

.050 

447 

.100 

224 

.055 

406 

oil  of  cinnamon  to  the  cooled  solution  prevents  souring.     Only  a 
few  drops  are  used  for  each  test. 

The  acetate  solution  is  made  by  dissolving  about  100  g. 
sodium  acetate  crystals  in  water,  adding  100  c.c.  acetic  acid  and 
making  up  to  one  litre  with  water.  About  10  c.c.  of  this  is  used 
for  each  test. 

TESTING  FOR  NITROGEN  OXIDES 

There  are  several  materials  about  a  chamber  plant  to  be  tested 
for  their  content  of  nitrogen  oxides.  The  nitrometer  method  is 
suitable  for  any  of  them  and  every  plant  should  have  one  in  use. 
This  instrument  can  be  had  in  several  different  forms  with  com- 

Plain  Leveling  Tube 


Graduated  Tubx? 


FIG.  60. 


pensating  attachments  but  for  the  control  work  about  a  chamber 
plant  the  simplest  form,  consisting  of  a  simple  graduated  burette 
with  thistle  top  and  two-way  stop  cock,  and  a  plain  levelling  tube, 
is  quite  satisfactory.  Figure  60  illustrates  this. 

The  nitrometer  method  depends  upon  the  fact  that  in  the  pres- 


TESTING  175 

ence  of  sulphuric  acid  mercury  will  react  with  nitric  acid  or  any  of 
the  nitrogen  oxides  above  N20,  to  form  Hg2S04and  NO,  a  colorless 
gas.  By  observing  the  volume  of  gas  derived  from  a  known  weight 
of  the  compound  to  be  examined,  its  nitric  acid  or  sodium  nitrate 
content,  or  equivalent,  can  be  calculated  at  0°C.  and  760  mm. 

1  c.c.  NO  =  .00281  g.  HNO3 
1  c.c.  NO  =  .00379  g.  NaN03 

In  performing  a  nitrometer  test  one  should  know  in  a  general 
way  the  amount  of  nitrogen  oxides  contained  in  the  material 
under  examination  and  should  figure  out  a  suitable  quantity  for 
introduction  into  the  nitrometer.  If  the  graduated  tube  is  of  50 
c.c.  capacity,  a  quantity  of  material  should  be  used  which  will 
evolve  a  volume  of  gas  preferably  between  25  and  50  c.c.  of  NO. 

The  nitrometer  is  prepared  by  opening  the  stop  cock  into  the 
reservoir  A  and  raising  the  levelling  tube  until  the  mercury  barely 
appears  in  the  bottom  of  A.  An  accurately  weighed  or  measured 
amount  of  the  material  under  examination  (in  solution  if  a  solid) 
is  put  into  A.  The  cock  is  slightly  opened  and  A  is  almost  but  not 
quite  drained.  Next  about  10  c.c.  of  concentrated  pure  sulphuric 
acid  is  put  into  A,  the  cock  opened  slightl/  and  the  acid  drawn 
into  B  as  completely  as  possible  without  drawing  in  air.  Tube  B 
is  now  well  shaken  for  about  two  minutes  to  bring  the  mercury  and 
the  solution  into  thorough  contact.  When  one  is  assured  that 
complete  reac  'don  has  taken  place  a  reading  is  taken  of  the  volume 
of  NO  which  has  been  evolved.  The  acid  in  B  has  a  specific 
gravity  about  %  that  of  mercury  so  to  observe  the  gas  volume 
under  atmospheric  pressure  the  reading  is  taken  with  the  mercury 
surface  in  C  held  at  a  point  above  the  mercury  surface  in  B  equal 
to  J<7  of  the  length  of  the  acid  column.  For  example,  if  the  acid 
column  is  14  c.c.  the  mercury  in  C  will  be  held  2  c.c.  above  the 
mercury  surface  in  B  when  the  reading  of  gas  volume  is  taken. 
A  correction  for  temperature  and  pressure  must  be  made  in  most 
cases.  It  is  sufficient  for  the  class  of  work  under  discussion 
to  determine  a  correction  factor  for  the  usual  room  temperature 
and  the  normal  barometer  and  to  use  this  factor  in  all  cases.  This 
factor  is  determined  by  the  following  formula: 

T> 

Factor  =  =77^  X 


760  ^  T+273 
B  =  Normal  barometer  in  m.m. 
T  =  Normal  temperature  in  degrees  Centigrade. 


176  AMERICAN  SULPHURIC  ACID  PRACTICE 

The  observed  gas  volume  is  multiplied  by  this  factor  and  the 
result  is  the  gas  volume  at  0°C.  and  760  mm.  pressure.  The 
materials  about  a  chamber  plant  to  which  the  nitrometer  test 
will  be  applied  are  nitrate  of  soda,  nitre  cake,  nitrous  vitriol  and 
mixed  acids. 

To  test  nitrate  of  soda,  dissolve  50  g.  in  water  and  make 
up  to  one  litre.  With  a  pipette  introduce  2  c.c.  into  the  nitro- 
meter and  perform  the  test  as  described. 

Per  cent  NaNO3  =  c.c.  NO  X  3.79 

To  test  nitre  cake,  dissolve  5  g.  in  water  and  make  up  to  25  c.c. 
With  a  pipette  introduce  5  c.c.  into  nitrometer  and  perform 
test  as  described. 

Per  cent  NaNO3  =  c.c.  NO  X  .379 

To  test  nitrous  vitriol  containing  not  over  70  oz.  NaNO3 
per  cu.  ft.,  introduce  2  c.c.  with  a  pipette  into  nitrometer  and 
proceed  as  described. 

Oz.  NaNO3  per  cu.  ft.  =  c.c.  NO  X  1.91 

To  test  mixed  nitric-sulphuric  acids,  it  is  usually  necessary 
to  dilute  with  concentrated  sulphuric  acid  in  order  to  avoid 
having  to  measure  an  exceedingly  small  quantity  for  use  in  the 
nitrometer.  It  is  not  well  to  try  to  use  less  than  2  c.c.  of  a  solu- 
tion for  test  as  pipettes  smaller  than  that  are  not  very  accurate. 

A  quick  method  of  estimating  the  amount  of  nitrogen  oxides 
in  nitrous  vitriol  is  by  a  titration  with  potassium  permanganate 
solution.  This  assumes  that  all  the  nitrogen  oxide  exists  as 
N203  and  reacts  thus: 

5N2O3  +  4KMn04  +  6H2SO4  =  2K2SO4  +  4MnSO4 
+  10HN03  +  H20 

Lunge  and  other  writers  on  this  subject  recommend  perform- 
ing this  test  by  measuring  a  known  amount  of  permanganate  into 
a  dish  and  running  in  nitrous  vitriol  from  a  burette  until  the 
permanganate  is  decolorized.  This  is  perhaps  slightly  more 
accurate  than  the  way  which  will  now  be  described. 

Fill  a  50  c.c.  burette  with  standard  permanganate  solution. 
Draw  a  little  water  into  a  porcelain  evaporating  dish  or  casserole 
and  run  into  it,  from  the  burette,  an  amount  of  permanganate 
slightly  less  than  needed.  Now  measure  into  the  dish  with  a 


TESTING  177 

pipette  5  c.c.  of  nitrous  vitriol.  This  should  decolorize  the 
permanganate.  If  it  does  not,  repeat,  using  less  permanganate. 
Next  add  permanganate  from  the  burette  until  a  faint  color, 
which  remains  on  stirring,  appears  in  the  dish. 

This  plan  is  much  more  convenient  than  the  first  described 
in  that  it  is  not  necessary  to  fill,  empty  and  clean  a  burette  for 
nitrous  vitriol  for  each  test.  It  very  closely  checks  the  first 
method  also.  It  is  convenient  to  use  a  permanganate  solution 
of  such  strength  that  1  c.c.  indicates  2  oz.  NaNO3  per  cu.  ft. 
of  nitrous  vitriol  when  using  5  c.c.  nitrous  vitriol  for  each  test. 
In  this,  if  the  nitrous  vitriol  carries  50  to  60  oz.  per  cu.  ft., 
there  will  be  drawn  25  or  30  c.c.  of  permanganate  for  each  test 
and  a  50  c.c.  burette  is  suitable  for  measuring  it.  Such  a  per- 
manganate solution  is  made  by  dissolving  7.44  g.  KMnOi  crystals 
in  water  and  making  up  to  one  litre. 

EXIT  GAS 

A  useful  though  rather  rough  test  to  determine  if  the  Gay 
Lussac  towers  are  functioning  well  mechanically  'is  made  by 
drawing  several  cubic  feet  of  exit  stack  gas  through  a  bulb  tube, 
partly  filled  with  60°  sulphuric  acid.  The  bulb  tube  is  shown  in 
Fig.  61.  It  is  charged  with  100  c.c.  of  60°  sulphuric  acid  and  the 


FIG.  61. 

gas  is  bubbled  through  it  for  several  hours.  Its  content  of 
nitrogen  oxides  is  then  determined  by  the  nitrometer.  This 
test  will  show  approximately  how  much  nitre  loss  is  being  suf- 
fered by  reason  of  insufficient  contact  between  the  gas  and  the 
acid  in  the  Gay  Lussac  towers.  Its  results  will  often  point  out 
poor  distribution  of  gas  or  acid  or  the  need  for  further  Gay 
Lussac  towers. 
12 


178 


AMERICAN  SULPHURIC  ACID  PRACTICE 


(| 


DRAFT  MEASUREMENTS 

It  is  desirable  to  observe  daily  the  gas  pressures  at  several 
points  in  the  chamber  system  to  be  certain  that  fans  are  working 
properly  and  that  no  obstructions  exist.  The  following  points 
certainly  should  be  examined;  entering  and 
leaving  the  Glover  tower,  before  and  after  each 
fan  and  entering  and  leaving  the  Gay  Lussac 
towers.  In  some  plants  further  observations 
may  be  necessary.  Two  instruments  are  most 
useful  for  this  work,  viz.,  the  small  diameter 
U  tube  and  the  Ellison  gage.  The  U  tube  is 
simply  a  glass  tube  of  J£  to  1  cm.  bore  bent  to 
a  U  shape  with  the  limbs  about  1  in.  apart. 
This  need  not  be  more  than  6  in.  long.  Behind 
this  is  placed  a  graduated  paper  scale  marked  in 
inches  and  tenths  or  in  millimeters.  One  limb 
of  this  tube  is  connected  to  the  flue  or  chamber 
whose  pressure  is  to  be  determined,  and  the 
other  left  open  to  the  atmosphere.  The  dif- 
ference between  the  level  of  water  in  the  two 
limbs  shows  the  difference  between  atmos- 
pheric  pressure  and  that  in  the  flue.  Figure 
62  illustrates  this. 

A  much  more  sensitive  instrument  is  the 
Ellison  gauge,  shown  in  Fig.  63.  It  is  suitable  for  measuring 
very  small  differences  of  pressure  as  well  as  measuring  considerable 
pressures  with  accuracy.  In  this  instrument  as  shown,  one  limb 


FIG  62 


Leveling  St 


FIG.  63. 


is  vertical  and  the  other  at  a  small  angle  with  the  horizontal. 
Any  movement  of  the  liquid  in  the  vertical  limb  is  accompanied 
by  a  movement  about  ten  times  as  long  in  the  sloping  limb  behind 


TESTING  179 

which  the  graduated  scale  is  placed.  The  Ellison  gauge  is  filled 
with  a  special  oil  colored  red  and  the  scale  with  which  it  is 
equipped  is  graduated  to  show  directly  hundredths  of  an  inch 
of  water  and  thousandths  can  be  fairly  accurately  estimated  by 
the  eye.  There  is  a  levelling  tube  on  the  case  and  the  base  is 
equipped  with  levelling  screws.  This  is  a  very  practical  and 
satisfactory  instrument. 

The  application  of  the  tests  described  will  be  taken  up  in  the 
chapter  -on  operation. 


CHAPTER  XV 

r 
OPERATION 

To  successfully  operate  a  chamber  acid  plant  one  should 
get  clearly  in  mind  the  chemical  and  physical  changes  undergone 
by  the  gas  mixture  in  its  course  through  the  plant.  One  must 
know  what  the  ideal  attainable  conditions  are  in  each  part  of 
the  plant  and  make  such  observations  as  are  necessary  to  know 
that  they  are  being  closely  approximated. 

First,  to  state  the  process  briefly  and  simply,  we  have  in  the 
normally  operating  plant  a  steady  uniform  amount  of  S02  com- 
ing into  the  chambers  and  moving  through  them  at  such  a  rate 
that  say  90  min.  are  occupied  in  the  passage  from  one  end  to 
the  other.  Such  an  amount  of  nitric  oxide  is  introduced  into  the 
gas  by  nitre  pots  and  in  the  Glover  tower  as  will  oxidize  sub- 
stantially all  of  the  S02  to  sulphuric  acid  in  that  90  min.  This 
amount  of  nitre  must  be  very  accurately  proportioned  or  results 
will  be  bad.  A  sufficient  amount  of  water  or  steam  must  be 
introduced  into  the  chambers  at  various  points  to  make  the  acid 
formed  therein  have  a  concentration  of  approximately  50°Be. 
The  Gay  Lussac  towers  through  which  the  residual  gas  from  the 
chambers  is  passed  must  be  fed  with  a  suitable  uniform  amount  of 
cold  60°Be.  sulphuric  acid  to  take  into  solution  85  to  90  per  cent 
of  the  nitrogen  compounds  existing  in  the  gas.  This  solution, 
the  "nitrous  vitriol,"  must  be  fed  back  uniformly  into  the  Glover 
tower  and  there  diluted  to  such  an  extent  that  the  hot  incoming 
gas  will  remove  and  carry  on  with  it  in  gaseous  form  all  of  the 
nitrogen  compounds.  This  is,  of  course,  the  main  source  of  the 
nitric  oxide  to  the  process,  constituting  by  simple  inference 
85  to  90  per  cent  of  the  amount  required.  The  other  10  to  15 
per  cent  is  supplied  by  potting  new  nitre  or  adding  nitric  acid. 

The  chemical  reactions  which  take  place  in  the  chamber 
process  have  been  subjects  of  much  controversy  and  there  is  still 
much  difference  of  opinion  concerning  some  of  them.  Without 
attempting  any  discussion  of  the  various  theories,  a  brief  state- 
ment of  the  ideas  of  Lunge  will  be  given.  These  may  or  may  not 

180 


OPERATION  181 

/ 

be  correctly  representative  of  the  chamber  process,  but  they 
give  a  good  basis  for  reasoning  and  are  very  well  borne  out  by 
the  phenomena  of  the  chambers. 

The  reactions  which  take  place  in  the  nitre  pots  or  the  retorts 
of  the  nitric  acid  plant  are : 

(1)  NaNO3  +  H2SO4    =  NaHSO4  +  HNO3 

(2)  NaHS04  +  NaNO3  =  Na2S04  +  HNO3 

The  first  reaction  takes  place  at  low  temperatures  and  the 
latter  at  higher  temperatures.  Nitre  cake  as  usually  made  is 
a  mixture  of  Na2S04  and  NaHSO4. 

In  the  Glover  tower,  nitric  acid  is  reacted  upon  thus: 

(3)  2HN03  +  3SO2  +  2HO2  =  3H2S04  +  2NO 

In  the  Glover  tower,  nitrous  vitriol  is  reacted  upon  thus 
"(denitration"): 

(4)  2HSN06  +  S02  +  2H20  =  3H2S04  +  2NO 

In  the  Glover  tower  this  reaction  probably  also  takes  place: 

(5)  2NO  +  2S02  +  H20  +  30  =  2HSN06 

In  the  Glover  tower  and  the  first  chambers  these  two  reactions 
4  and  5  are  the  predominating  ones.  The  only  oxide  of  nitrogen 
which  exists  in  quantity  is  NO.  This  is  a  colorless  gas  which 
explains  the  fact  that  front  chamber  gases  show  little  red 
color. 

As  the  gas  mixture  becomes  leaner  in  SO2  the  folio  wing  reactions 
take  place: 

(6)  2HSNO6  +  H2O  =  2H2S04  +  N203 

(7)  N203  +  2S02  +  20  +  H20  =  2HSN05 

These  two  reactions  take  place  more  and  more  as  the  gas 
approaches  the  last  chamber.  The  predominating  oxide  of 
nitrogen  is  N2O3  (probably  a  mixture  of  NO  and  N02),  which  is 
a  red  gas  and  which  gives  the  gas  mixture  its  red  color. 

If  conditions  are  ideal,  the  gas  mixture  entering  the  Gay 
Lussac  tower  contains  substantially  all  its  nitrogen  oxide  as  N2O3 
or  equal  parts  of  NO  and  NO2.  This  is  absorbed  by  the  sulphuric 
acid  in  the  Gay  Lussac  packing  thus : 

(8)  N203  +  2H2S04  =  2HSNO5  +  H20 

If  an  excess  of  NO  exists  it  is  not  absorbed  by  the  Gay  Lussacs. 
This  condition  exists  when  there  is  a  considerable  amount  of  SOg 


182  AMERICAN  SULPHURIC  ACID  PRACTICE 

in  the  gas  mixture  entering  the  Gay  Lussacs.  If  an  excess  of 
NO2  exists,  it  partly  reacts  with  the  sulphuric  acid  in  the  Gay 
Lussacs  thus: 

(9)  2N02  +  H2S04  =  HN03  +  HSN05 

This  reaction  is  not  complete  and  some  NO 2  goes  through  and 
shows  as  a  red  cloud  at  the  Stack.  This  condition  exists  when  an 
undue  amount  of  nitre  is  introduced  with  the  entering  gas  and 
the  S(>2  is  completely  converted  to  sulphuric  acid  sometime 
before  the  gas  reaches  the  Gay  Lussacs. 

The  time  of  passage  of  the  gas  through  the  chambers  is  some- 
thing which  varies  in  different  plants  and  which  depends  upon 
the  style  of  work  done.  In  some  chamber  plants  the  period  is  as 
short  as  1  hour  and  in  others  more  than  2  hours.  It  is  simple  to 
calculate  from  the  S02  analyses,  the  make  of  acid  and  the  volume 
of  the  chambers  what  the  period  is.  This  should  be  known  by  the 
operator.  The  amount  of  nitre  necessary  to  be  introduced  for 
normal  work  is  also  dependent  on  the  individual  characteristics 
of  the  plant  and  upon  the  style  of  work.  In  modern  American 
plants,  an  average  amount  is  probably  25  to  30  parts  sodium 
nitrate  for  each  100  parts  sulphur.  For  example,  if  100  tons  60° 
acid  is  made  per  day,  the  sulphur  in  the  SO2  used  is  approximately 
25  tons  or  50,000  Ib.  The  sodium  nitrate  equivalent  of  the 
nitrous  vitriol  plus  the  new  nitre  will  amount  to  25  or  30  per  cent 
of  50,000  Ib.,  or  12,500  to  15,000  Ib. 

If  absolute  uniformity  of  all  the  factors  of  the  process  could  be 
maintained,  the  operation  would  be  very  simple.  Involving 
as  it  does  high  temperature,  dusty,  corrosive  gas  and  sulphuric 
and  nitric  acids,  many  irregularities  occur  and  it  is  in  meeting 
them  properly  that  the  skill  in  operating  lies.  It  is  of  course, 
much  simpler  to  operate  a  plant  deriving  its  gas  from  brimstone 
burning  than  to  operate  one  on  blast  furnace  gas  or  some  of  the 
other  metallurgical  by-product  gases. 

In  years  gone  by,  chamber  acid  plants  were  almost  entirely 
operated  by  rule  of  thumb  methods.  Operators  by  considerable 
periods  of  experience  became  often  very  skilled  in  handling  the 
process,  depending  upon  such  observations  as  color  of  the  gas 
mixture  in  the  chambers,  effervescence  of  nitrous  vitriol  on  dilu- 
tion with  warm  water  and  various  other  equally  inexact  phe- 
nomena. The  old  hand  at  the  business  did  well  sometimes  but 
several  years  were  necessary  to  make  an  old  hand.  In  recent 


OPERATION  183 

years,  particularly  since  metallurgical  gases  have  come  to  be 
used  to  a  considerable  extent,  more  exact  methods  are  being 
employed,  for  control  of  the  acid  process.  It  is  true  that  there 
are  plants  still  operated  by  the  old  plan,  but  certainly  better 
work  can  be  done  in  any  plant  by  making  accurate  observations 
and  records. 

The  thing  of  chief  importance  in  the  chamber  process  is  the 
proper  proportioning  of  nitre  to  SO2.  The  amount  of  nitre 
derived  from  the  nitrous  vitriol  and  from  the  nitre  pots  or  fresh 
nitric  acid  must  at  any  given  time  be  precisely  enough  and  not  too 
much,  to  convert  substantially  all  of  the  S02  coming  in  at  that 
time  to  sulphuric  acid  during  the  period  of  passage  of  that  gas 
through  the  chambers.  If  the  amount  of  nitre  is  not  sufficient 
all  of  the  S02  will  not  be  converted  to  sulphuric  acid.  The  SOz 
remaining  unconverted  will  pass  out  and  be  lost.  The  nitrogen 
compounds  will  exist  as  N02  and  NO  with  NO  in  excess  and  as 
NO  is  not  absorbed  by  the  Gay  Lussac  towers,  that  excess  will 
be  lost.  There  will  be  loss  of  both  sulphur  and  nitre.  If  the 
amount  of  nitre  introduced  be  too  much,  there  will  be  no  loss 
of  SO2. 

The  SO2  will  all  be  converted  to  sulphuric  acid  some  time  before 
the  gas  mixture  finishes  its  passage  through  the  chambers  and 
during  that  time,  oxidation  of  the  NO  present  will  proceed  and  the 
gas  entering  the  Gay  Lussacs  will  contain  N02  and  NO  with  NO2 
in  excess.  N02  is  partly  but  not  completely  absorbed  by  the 
Gay  Lussac  towers  and  the  part  that  is  not  absorbed  passes  out 
into  the  atmosphere  as  a  red  cloud.  In  the  absorption  some 
nitric  acid  is  formed  which  is  not  particularly  good  for  the  lead. 
From  these  statements  it  can  be  understood  that  nitre  loss  occurs 
if  the  amount  of  nitre  originally  introduced  be  either  too  large 
or  too  small  to  completely  convert  its  accompanying  S02  in  just 
the  proper  time. 

The  original  establishment  of  these  conditions  is  done  by  trial. 
To  maintain  them,  the  modern  acid  maker  depends  mainly  upon 
periodical  observation  and  recording  of  the  temperatures  in  the 
chambers  at  many  points  throughout  the  system,  and  upon  period- 
ical determinations  of  SO2  in  the  gas  mixture  at  a  point  just 
preceding  or  following  the  Glover  tower,  and  at  another  point 
just  preceding  the  Gay  Lussac  tower.  There  are  other  indica- 
tions which  are  made  of  use  to  some  extent  such  as  the  concen- 
tration and  appearance  of  the  chamber  drips,  the  color  of  the  gas, 


184  AMERICAN  SULPHURIC  ACID  PRACTICE 

the  appearance  of  the  exit  stack,  the  nitrous  vitriol  determina- 
tions, etc.,  but  these  are  used  more  to  confirm  the  temperature 
and  SO2  knowledge  than  anything  else. 

To  illustrate  in  a  concrete  way  how  these  observations  are  used, 
we  will  assume  that  hourly  observations  and  records  are  made  of 

1.  Temperature  and  °Be.  of  drip  on  each  chamber. 

2.  SC>2  in  gas  entering  Glover  tower. 

3.  SO2  in  gas  entering  Gay  Lussac  towers. 

4.  Nitrous  vitriol. 

5.  Atmospheric  temperature. 

The  operator  comes  on  and  immediately  makes  a  set  of  rec- 
ords as  above.  If  the  percentage  of  S02  in  the  gas  entering  the 
Gay  Lussac  towers  is  correct  he  knows  that  90  min.  before,  the 
nitre  was  properly  proportioned  to  the  SO2.  He  looks  back  on 
his  record  sheets  and  observes  that  at  that  time  the  S02  entering 
the  Glover  was  say  8.0  per  cent  and  that  the  temperature  of  the 
front  chamber  was  195°F.  If  the  gas  entering  the  Glover  is  still 
8.0  S02  he  can  reasonably  assume  that  the  front  chamber  tem- 
perature should  be  within  a  degree  of  195°F.  If  it  is  much  under 
195°F.  the  amount  of  nitre  entering  is  deficient  and  if  much  over 
195°F.  the  nitre  feed  is  more  than  necessary.  If  the  SO2  in  the 
gas  entering  the  Glover  has  decreased  to  say  7.6  per  cent  the  oper- 
ator will  know  by  experience  that  his  front  chamber  temperature 
should  be  somewhat  less  than  195°F.,  say  190°F.  If  on  the  other 
hand,  the  gas  entering  the  Glover  has  increased  to  say  8.2  per  cent 
he  will  know  that  his  front  chamber  temperature  should  be  per- 
haps 197°  or  198°F.  He  will  in  the  one  case  decrease  the  nitrous 
vitriol  stream  slightly  and  continue  such  adjustments  until  the 
desired  temperature  is  attained.  The  correctness  of  the  oper- 
ators adjustments  will  be  shown  by  the  SO2  determination  at 
the  Gay  Lussacs  90  min.  later.  This  system  of  observation  and 
adjustment  is  carried  out  constantly  and  if  faithfully  attended  to, 
produces  excellent  results. 

A  further  elaboration  of  the  plan  of  control  by  S02  tests  has 
been  proposed  and  carried  out  successfully  by  A.  M.  Fairlie. 
This  plan  is  as  follows:  An  SO2  test  is  made  at  a  point  near  the 
Glover  tower.  A  short  time  later  an  S02  test  is  made  at  another 
point  some  little  distance  along  say  at  the  end  of  the  leading 
chamber.  The  time  between  the  tests  is  approximately  that 
occupied  by  the  gas  in  passing  between  the  two  test  points.  As- 


OPERATION  185 

suming  uniform  gas  velocity,  for  any  given  862  percentage  at  the 
first  point  there  is  a  certain  proper  S02  percentage  at  the  second 
point  to  assure  perfect  conditions  at  the  entrance  to  the  Gay 
Lussacs.  It  the  S02  at  the  second  point  is  not  correct,  an  adjust- 
ment in  the  nitre  feed  is  made.  This  is  a  most  excellent  method 
of  control  and  in  certain  cases  where  the  gas  supply  fluctuates 
widely,  its  practical  value  is  high. 

Control  of  the  nitre  feed  lies  in  two  things,  the  nitrous  vitriol 
and  the  nitre  pots,  or  the  nitric  acid.  Of  the  total  the  nitre 
derived  from  the  nitrous  vitriol  amounts  to  between  85  and  90 
per  cent,  and  the  added  or  new  nitre  to  10  to  15  per  cent.  It  is  a 
very  good  plan  to  decide  upon  a  suitable  amount  of  new  nitre  to 
be  used  at  the  beginning  of  each  shift  and  to  maintain  it  constant 
throughout  the  shift,  barring,  of  course,  large  irregularities. 
The  minor  changes  necessary,  such  as  the  ones  specified  above  are 
taken  care  of  by  changing  the  flow  of  nitrous  vitriol.  This  can 
be  accomplished  readily  by  means  of  a  long  distance  control 
arrangement.  If  the  frequent  small  changes  desirable  are  made 
by  varying  the  amount  of  nitre  potted,  the  potting  schedule 
becomes  very  intricate.  If  it  is  done  by  varying  the  flow  of  new 
nitric  acid,  many  trips  to  the  top  of  the  Glover  tower  are  neces- 
sary as  it  is  hardly  feasible  to  make  nice  changes  in  a  stream  of 
liquid  ranging  from  knitting  needle  to  pencil  size  with  any  long 
distance  methods.  The  nitrous  vitriol,  on  the  other  hand,  is  a 
rather  ample  flow,  and  its  nitre  content  is  low  so  that  its  control 
is  very  convenient. 

To  illustrate  by  an  example,  suppose  a  system  running  normally 
with  8  per  cent  gas  and  proper  nitre  feed  of  which  87  per  cent  is 
from  the  nitrous  vitriol  and  13  per  cent  new  nitre.  The  gas 
decreases  to  7.6  per  cent,  i.e.,  5  per  cent.  The  nitre  feed  should 
be  decreased  5  per  cent.  This  can  be  done  by  decreasing  the 
nitrous  vitriol  flow  by  5.75  per  cent  (since  5  per  cent  is  5.75  per 
cent  of  87).  If  the  change  is  made  by  varying  the  new  nitre,  this 
will  have  to  be  decreased  by  38.5  per  cent(since  5  is  38.5  per 
cent  of  13).  With  suitable  tank  space  for  nitrous  vitriol,  these 
minor  changes  are  not  often  reflected  back  to  the  Gay  Lussac 
towers  which  go  on  running  with  constant  flows. 

To  decide  upon  the  amount  of  new  nitre  to  be  used  for  a  shift, 
the  operator  will  observe  the  stock  of  nitrous  vitriol  in  the  tanks 
and  whether  the  nitrous  vitriol  is  of  normal  grade.  If  the  stock 
is  right  and  the  nitrous  vitriol  normal  he  will  establish  or  con- 


186  AMERICAN  SULPHURIC  ACID  PRACTICE 

tinue  the  introduction  of  the  normal  amount  of  new  nitre.  If 
the  stock  is  low  or  the  nitrous  vitriol  below  normal  in  nitre  content, 
he  will  establish  a  rate  of  introduction  of  new  nitre  somewhat 
above  normal  in  order  to  bring  the  nitrous  vitriol  stock  and  grade 
back  where  it  belongs.  If,  on  the  other  hand,  stock  or  grade  of 
nitrous  vitriol  are  above  normal,  he  will  have  an  opportunity  to 
run  with  less  than  the  normal  feed  of  new  nitre. 

The  drips  on  the  chambers  are  tested  hourly.  They  should 
be  kept  between  48°  and  50°Be. — not  higher,  because  the  nitrogen 
compounds  begin  to  be  taken  into  solution,  and  not  lower,  be- 
cause concentration  capacity  of  the  Glover  tower  will  be  over- 
taxed. The  control  of  the  acid  strength  lies  in  the  amount  of 
water  or  steam  admitted  to  the  chambers.  Ordinarily  the  hy- 
drometer readings  are  taken  without  correcting  for  temperature, 
although  for  strict  accuracy,  corrections  up  to  .5°Be.  should  be 
added.  The  bottom  acid  in  a  chamber  is  always  slightly  higher 
in  strength  than  the  drip. 

The  acid  issuing  from  the  Glover  tower  coolers  should  be  ob- 
served several  times  a  day  -for  strength  and  temperature.  It 
should  ordinarily  be  kept  between  59°  and  61°  after  applying  the 
temperature  correction.  The  minimum  represents  the  lowest 
proper  strength  for  Gay  Lussac  feed.  Above  61°  there  exists 
danger  of  incomplete  denitration  in  the  Glover  unless  the  burner 
gas  is  very  hot.  The  temperature  of  the  acid  issuing  from  the 
cooler  should  be  not  over  80°F.  and  preferably  less.  From  time 
to  time,  the  coils  in  the  cooler  become  encrusted  and  when  the 
acid  temperature  rises  above  80°F.  the  cooler  should  be  drained 
and  washed  out  with  a  hose.  It  is  well  to  test  this  acid  from  time 
to  time  by  the  nitrometer  to  be  certain  that  no  nitre  is  being 
retained  by  the  acid.  If  denitration  is  not  complete,  the  feed  of 
weak  acid  on  the  Glover  must  be  increased. 

The  nitrous  vitriol  issuing  from  the  first  Gay  Lussac  tower  is 
tested  with  potassium  permanganate  once  an  hour.  Any  great 
variation  from  the  normal  should  be  accounted  for.  This 
normal  nitrous  vitriol  is  something  which  will  be  decided  upon 
for  each  system.  It  is  right  in  one  plant  to  run  with  perhaps  35 
oz.  NaNOs  per  cubic  foot  and  in  another  with  70  oz.  or  more. 
Several  considerations  enter.  The  amount  of  absorbable  nitre 
entering  the  Gay  Lussacs  in  a  given  system  will  be  fairly  con- 
stant. The  nitre  content  of  the  nitrous  vitriol  will  then  depend 
upon  the  amount  of  acid  fed  to  the  Gay  Lussac  tower.  The 


OPERATION  187 

smallest  permissible  amount  is  that  which  can  be  divided  and 
distributed  over  the  packing  with  sufficient  thoroughness  to 
assure  wetting  the  entire  area.  If  any  of  the  packing  remains 
dry,  or  nearly  so,  the  nitre  laden  gas  will  pass  through  that  part 
of  the  tower  without  having  the  nitre  recovered  from  it.  A  good 
safe  quantity  to  assure  wetting  is  one  ton  of  acid  per  square  foot 
of  horizontal  area  per  24  hours.  If  the  tower  has  for  example,  an 
area  of  200  sq.  ft.,  about  200  tons  per  day  should  be  put  over  it. 
This  quantity  may  be  exceeded  and  assurance  of  complete  wetting 
made  doubly  sure,  but  a  greater  amount  than  that  mentioned  is 
not  necessary.  If  the  plant  served  by  this  tower  makes  100 
tons  60°  acid,  the  nitre  entering  the  Gay  Lussac  tower  will 
amount  to  about  12,500  Ib.  NaNO3  and  if  87  per  cent  recovery  is 
made,  the  normal  nitrous  vitriol  will  be  45  to  46  oz.  per  cubic 
foot. 

If,  as  in  many  plants,  the  horizontal  area  of  the  Gay  Lussac 
towers  is  proportionally  less,  a  smaller  acid  circulation  will  be 
used  and  nitrous  vitriol  of  higher  nitre  content  produced. 

In  any  event,  a  proper  normal  will  be  established  and  any  wide 
variation  from  it  indicates  an  irregularity  in  process,  or  acid 
flow. 

An  observation  and  record  of  drafts  should  be  made  once  a  day 
by  the  instruments  already  described.  Any  important  variation 
from  normal  should  be  investigated.  Sometimes  in  a  Glover 
tower,  for  example,  there  will  be  a  very  gradual  increase  in  the 
packing  resistance  indicated  by  an  increase  in  the  difference 
between  the  pressures  at  bottom  and  top.  This  indicates  usually, 
the  accumulation  of  sediment  or  dust  in  the  packing,  and  when 
it  reaches  a  certain  point,  flushing  out  is  necessary. 

LABOR  FORCE 

The  number  of  men  required  to  operate  a  chamber  plant  is 
small,  but  care  and  reliability  are  absolutely  essential.  In 
order  to  give  an  idea  of  the  normal  labor  force  required,  assume 
a  100-ton  unit  having  mechanical  burners,  flue  nitre  pots  and 
acid  eggs  for  pumping.  There  will  be,  on  each  shift,  one  furnace- 
man,  one  nitreman,  one  pumpman  and  a  chamberman  who 
exercises  general  supervision.  On  the  day  shift  will  be  a  repair- 
man and  two  laborers.  This  force  may  be  reduced  in  certain 
small  plants  by  having  the  furnaceman  attend  the  nitre  potting 


188  AMERICAN  SULPHURIC  ACID  PRACTICE 

as  well  as  the  furnaces.  In  case  a  nitric-acid  or  mixed  acid  plant 
is  used  instead  of  flue  pots,  one  man  will  produce  enough  nitric 
acid  in  one  shift  to  run  the  plant  24  hours. 

The  whole  operation  should  be  supervised  by  a  man  of  experi- 
ence and  judgment.  It  is  a  false  economy  to  run  even  a  modest 
sized  plant  without  such  a  man. 


CHAPTER  XVI 
CONCENTRATION 

Sulphuric  acid  made  in  the  chambers  is  only,  at  its  best,  52°  to 
53°Be.,  and  where  an  acid  of  greater  concentration  is  required 
it  is  necessary  to  concentrate  this  chamber  acid.  There  are 
various  methods  of  doing  this. 

Before  the  introduction  of  the  Glover  tower,  chamber  acid  was 
concentrated  in  lead  pans,  up  to  60°  or  61°Be*.  Since  the  Glover's 
introduction  it  has  been  an  easy  matter  for  manufacturers  to 
bring  their  chamber  acid  up  to  61°Be.  in  the  tower,  as  described 
under  that  subject. 

Lead  pans  are  still  used  in  old  works  that  have  no  Glover 
tower,  and  in  concentrating  waste  acid. 

The  vapor  from  boiling,  dilute  sulphuric  acid  consists  almost 
entirely  of  water  vapor:  therefore,  the  acid  will  become  more 
and  more  concentrated,  as  the  boiling  proceeds,  as  long  as 
60°Be.  is  not  exceeded. 

In  pan  concentration  lead  pans  are  almost  universally  used  for 
the  concentration  of  acid  up  to  60°Be.  Above  this  point,  lead 
is  acted  upon,  necessitating  the  use  of  other  material. 

Pans  may  be  heated  by  direct  flame,  either  from  the  top  or 
bottom,  by  steam,  or  by  the  waste  heat  from  pyrites  or  sulphur 
burners. 

When  the  purity  or  appearance  of  the  acid  is  of  less  importance 
than  the  saving  in  fuel,  or  in  labor,  top  firing  is  generally  used. 
The  pans  are  generally  30  ft.  long,  4  ft.  11  in.  wide,  with  sides 
17  in.  high.  They  are  built  from  heavy  lead,  15  to  30  Ib.  to  the 
sq.  ft.,  and  always  in  one  piece;  the  corners  are  never  cut,  but 
are  folded  over. 

It  is  necessary  to  protect  the  lead  from  the  direct  action  of  the 
fire.  The  fire  box  is  always  built  separate  from  the  pan,  and  is 
only  connected  to  it  by  an  arch  which  extends  the  length  of  the 
pan,  and  a  fire-proof  clay  slab  at  the  bottom.  The  pan  inside  is 
protected  by  acid-proof  bricks  or  slabs.  At  the  long  side  these 
extend  up  to  the  arch,  while  on  the  short,  or  fire  side,  they  only 
reach  to  the  top  of  the  pan,  and  there  is  placed  the  fire-proof 

189 


190  AMERICAN  SULPHURIC  ACID  PRACTICE 

slab  to  the  fire  box.  There  are  openings  left  in  the  bottom  of  the 
partition  slabs,  so  the  acid  can  circulate  freely.  The  pan  is 
always  raised  3  ft.  or  more  above  the  ground. 

The  acid  is  introduced  at  the  end  nearest  the  fire  box,  and 
drawn  out  at  the  far  end.  Evaporation  is  very  rapid,  both 
because  the  hot  gases  come  into  direct  contact  with  the  acid,  and 
because  the  chimney  draught  carries  away  the  water  formed. 
The  damage  to  the  pans  is  very  slight,  as  the  brick  lining  protects 
the  lead  from  direct  heat,  and  up  to  60°,  or  even  61°Be.  the  acid 
has  very  little  effect  upon  lead.  But  above  that  degree  of  con- 
centration not  only  does  the  acid  act  upon  lead,  but  its  boiling 
point  gets  close  to  the  temperature  at  which  lead  begins  to 
soften. 

Keeping  the  acid  at  a  constant  level  also  protects  the  pans. 
Except  for  repairs  the  acid  is  never  drawn  off  entirely,  but  as 
the  concentrated  acid  sinks  and  is  drawn  off  from  the  bottom 
fresh  weak  acid  is  added  at  the  top.  Efforts  at  water  cooling 
have  not  been  successful,  as  lead  pipes  or  jackets  start  leaking 
easily,  and  cause  trouble. 

The  greatest  destructive  effect  is  at  the  fire  end  of  the  pan,  and 
to  keep  it  as  cool  as  possible  the  weak  acid  is  added  here,  through 
a  pipe  through  the  arch.  The  syphon  to  withdraw  concentrated 
acid  is  at  the  cool  end  of  the  pan,  but  even  then  the  acid  is  too 
hot  to  use,  and  is  run  into  shallow  lead  cooling  pans,  stayed  with 
wood  or  iron  frames. 

If  the  pans  need  staying  it  should  be  done  by  cast-iron  or 
pressed-steel  grids,  as  their  large  radiating  surface  will  help  keep 
the  lead  cool. 

Coal  used  will  vary  from  2  per  cent  to  10  per  cent  by  weight  of 
the  acid  concentrated,  varying  with  quality  of  coal  and  size  of 
pan.  A  long  pan  is  most  economical. 

One  square  foot  of  pan  surface  will  concentrate  150  Ib.  of 
chamber  acid  to  61°Be.  per  24  hours. 

The  strength  of  concentrate  is  regulated  by  the  fire  and  the 
weak  acid  fed. 

No  data  is  available  as  to  the  loss  of  acid  in  this  method  of 
concentration,  but  it  is  probably  more  than  for  bottom-heated 
pans,  as  the  stream  of  hot  gases  carries  away  acid  in  minute 
drops,  that  are  very  hard  to  condense.  We  meet  this  same  mist 
in  the  contact  process,  and  it  gives  us  the  same  trouble. 

The  spray  of  acid  from  the  stacks  is  not  only  a  loss,  but  a 


CONCENTRATION 


191 


nuisance,  and  sometimes  the  basis  of  suits  by  neighboring 
property  owners.  Gas,  instead  of  coal,  firing  has  been  tried  as 
a  remedy,  without  much  success,  and  the  only  relief  has  come 
from  the  use  of  higher  stacks,  causing  a  better  diffusion  in  the  air. 

Lead  pans  heated  from  below  are  always  smaller  than  those 
using  "top  fire,"  and  are  built  in  sets.  The  reason  for  this  is 
that  the  pans  nearer  the  fire  are  worn  out  first,  and  it  is  cheaper 
to  have  a  small  pan  to  replace.  The  concentration  is  very  regular, 
the  weak  acid  flowing  in  at  one  end,  and  running  from  one  pan 
to  the  next,  until  it  runs  off  sufficiently  strong  at  the  other  end. 

The  pans  are  rectangular,  5  to  7  ft.  on  a  side,  and  about  15  in. 
deep.  There  are  four  to  six  in  a  set.  The  acid  is  carried  from 
pan  to  pan  by  overflow  pipes,  so  that  it  takes  the  acid  from  the 
bottom  of  one  pan  to  the  top  of  the  next,  as  the  acid  is  stronger 
at  the  bottom.  The  flow  of  weak  acid  is  so  regulated  that  the 
proper  concentration  of  acid  is  obtained  at  the  last  pan. 

The  pan  bottoms  are  protected  from  the  fire  by  iron  plates, 
these  plates  being  heavier  at  the  fire  end.  The  iron,  being  a 
good  conductor  of  heat,  also  assists  the  heat  distribution.  Some- 
times copper  plates  are  placed  between  the  pan  bottom  and  the 
iron  plate  to  prevent,  by  their  good  conducting  qualities,  local 
overheating  and  buckling  of  the  pan. 

The  general  plan  is  to  place  the  fire  under  the  weak  pan.  In 
this  way  the  strong  pan  does  not  receive  much  more  damage 
than  the  others,  and  evaporation  goes  on  satisfactorily  as  well. 
The  old  practice  was  to  place  the  fire  under  the  strong  pan, 
because  the  boiling  point  of  the  strong  acid  is  the  highest,  but 
on  account  of  the  wear  on  the  pan  it  has  been  found  more 
economical  to  reverse  the  operation. 

Bode  gives  the  following  table,  where  the  fact  that  the  greatest 
heating  takes  place  at  the  third  pan  shows  that  the  fire  is  badly 
utilized : 


Acid  running  in  .... 



1st 
pan 

2nd 
pan 

3rd 
pan 

4th 
pan 

5th 
pan 

6th 
pan 

Temperature  

25° 

112° 

150° 

160° 

148° 

145° 

143°C. 

Strength  .    . 

110° 

113° 

120° 

128° 

134° 

140° 

144°  Tw. 

Temperature  
Strength  

24° 
110° 

110° 
113° 

145° 
118° 

156° 
126° 

145° 
134' 

142° 
140C 

142°C. 
144°  Tw. 

192  AMERICAN  SULPHURIC  ACID  PRACTICE 

He  estimates,  for  English  practice  (1910),  that  a  set  of  six  pans 
will  cost  $500,  and  the  maintenance  will  be  12  per  cent.  Total 
cost  of  concentration  55^  to  65^  per  ton. 

Coal  required  is  about  15  per  cent  of  the  weight  of  the  acid 
concentrated,  and  each  squae  foot  of  pan  area  will  produce  85  Ib. 
of  60°  acid  every  24  hours. 

Pans  for  utilizing  waste  heat  from  pyrites  or  brimstone  burners 
must  be  designed  for  each  special  case,  the  principles  being  the 
same  as  for  bottom-heated  pans.  Sometimes  the  pans  are 
placed  over  the  dust  flue,  but  protected  from  the  direct  action  of 
the  burner  gases  by  brick,  or  often  over  the  burners  themselves. 
This  method  of  concentrating  is  very  cheap,  requiring  only  part 
of  a  man's  time,  and  the  maintenance  charges,  Bode  says, 
10^  to  18^  per  ton  (1910). 

Steam  pans  are  of  many  forms,  all  depending  upon  slow 
evaporation  far  below  the  boiling  point  of  the  pan  acid.  Steam 
is  introduced  through  a  lead  coil,  which  lies  on  the  bottom  of  the 
pan,  the  condensation  returning  from  it  to  the  boiler.  There  is 
no  acid  mist  escaping,  so  no  injury  to  vegetation  is  possible; 
but  steam  coil  concentration  is  so  expensive  that  the  writer  does 
not  know  of  a  single  installation  in  the  United  States. 

QUALITY  OF  LEAD 

Lead  as  heavy  as  that  used  for  concentrating  pans  is  difficult 
to  bend  cold,  so  a  light  fire  of  shavings  is  made  on  the  part  of 
the  lead  plate  to  be  bent,  and  the  lead  softened  sufficiently  to 
be  easily  manipulated. 

W.  B.  Hart,  Journal  of  the  Chemical  Society,  1907,  writes  as 
follows: 

Lead  may  fail  from  either  or  both  chemical  or  physical  faults  : 

The  effects  of  impurities  are  as  follows: 

(a)  With  bismuth  and  tin,  lead  forms  alloys  of  low  fusibility, 
causing  local  perforation.     Acid  may  concentrate  in  these  leaks, 
and  become  strong  enough  to  attack  the  lead  itself. 

(b)  Aluminum,  tin,  or  zinc  may  cause  sudden  failure  at  certain 
stages  of  the  concentration. 

(c)  The  physical  condition  of  zinc  will  sometimes  increase  the 
chemical  action  of  acid  upon  lead. 

(d)  Electrolytic  action  may  be  set  up  between  deposits  of 
impurities  and  the  lead. 


CON  C  EN  TRA  TION  193 

(e)  Antimony  may  have  a  strong  and  harmful  chemical  effect, 
and  copper,  arsenic,  and  silver  very  little.  Copper  may  even 
be  helpful  under  certain  conditions.  By  constant  use  copper 
may  be  entirely  dissolved  out,  and  its  corrosive  effect  upon  other 
impurities  lost.  This  will  sometimes  explain  the  sudden  failure 
of  a  pan  that  has  been  in  good  condition  for  a  long  time. 

(/)  Pure  lead,  under  normal  pan  conditions,  is  undoubtedly 
less  affected  than  the  impure  metal. 

Faulty  physical  conditions  may  be  due  to  bad  remelting,  use 
of  unsuitable  casting  temperatures,  and  too  severe  pressure  in  the 
rolling  operation. 

(a)  Production  of  a  loose  crystalline  structure,  by  casting  the 
metal  at  too  high  a  temperature,  causing  leakage. 

(6)  Production  of  a  surface  more  susceptible  to  attack,  by  too 
severe  pressure  during  rolling. 

(c)  Strong  acid  action  in  the  temporarily  physically  altered 
form  of  lead,  before  the  annealing  effect  can  take  effect,  explains 
the  failure  of  pans  that  have  been  in  use  a  very  short  time. 

(d)  Altered  physical  condition  can  make  unsuitable  even  a 
lead  of  exceptionally  pure  chemical  composition. 

CONCENTRATION  FROM  60°  TO  66° 

Concentration  of  sulphuric  acid  naturally  resolves  itself  into 
three  divisions — first,  chamber  to  60°Be.;  second,  60°to66°Be., 
or  "93.19"  (per  cent),  as  it  is  often  called,  and  from  93.19  per 
cent  H2SO4  up  to  97.50  or  98  per  cent  H2SO4. 

Ordinary  pan  concentration,  as  just  described,  is  the  usual  first 
step.  For  the  second  several  methods  are  used,  and  are  presented 
in  what  the  writer  considers  their  order  of  merit. 

First,  because  very  simple  and  efficient,  comes  the  "heat  ex- 
changer." As  applied  at  one  large  works,  this  is  a  continuation 
of  the  lead  pans. 

A  series  of  five  lead  pans  concentrates  the  acid  to  62°Be.,  and 
the  acid  leaves  the  last  lead  pan  at  a  temperature  of  from  285°  to 
320°F.,  practically  the  temperature  of  the  first  pan.  The  highest 
temperature  usually  comes  in  the  third  pan. 

From  the  last  lead  pan  the  acid  flows  to  a  pulsometer,  or  air 
lift,  which  raises  it  to  the  top  of  the  heat  exchanger.  The  heat 
exchanger  is  a  lead-lined  steel  tower,  further  lined  with  three 
courses  of  acid-resisting  brick,  and  filled  with  broken  quartz.  It 

13 


194 


AMERICAN  SULPHURIC  ACID  PRACTICE 


is  12  ft.  high,  and  21  in.  in  diameter  inside  the  brick.  The  acid 
trickles  down  through  the  broken  quartz  packing,  and  meets  the 
ascending  gases,  rich  in  SOs,  from  the  covered  iron  pan,  which  is 
set  directly  over  the  flame.  The  falling  acid  is  cool  enough  to 
absorb  practically  all  of  the  SOs  in  the  ascending  gas,  and  while 
it  does  take  up  some  of  the  moisture  driven  off  too,  it  is  not 
enough  to  hinder  the  concentrating  operation.  The  unabsorbed 
gas,  now  almost  entirely  steam,  passes  from  the  top  of  the  heat 
exchanger  to  two  lead-lined  condensing  towers,  filled  with  coke, 


Section  B-B 
•Acid 


Section  A -A 


Pulsometer 


Jower 


Lead  Pans, 


Air' 


Iron  Pan  - 


Qrate- 


FIG.  64. 

which  catches  any  drops  of  acid.  The  passage  of  the  gases 
through  the  heat  exchanger  and  condensing  towers  is  induced  by 
a  steam  jet,  attached  to  the  exit  flue  of  the  second  tower. 

From  the  bottom  of  the  heat  exchanger  the  acid,  enriched  by 
the  SO3  absorbed,  flows  to  the  iron  pan,  where  it  is  concentrated 
to  66°Be.,  and  is  then  syphoned  off  to  a  tant-iron  box,  equipped 
with  cooling  coils  of  lead,  where  it  is  cooled  down  to  80°F. 
Thence  it  goes  to  storage. 

The  temperature  of  the  iron  pan  is  unheeded.  The  first  lead 
pan  is  kept  at  285°  to  310°F.,  and  upon  the  fire  necessary  to 
accomplish  this  depends  the  degree  of  heat  of  the  iron  pan. 


CONCENTRATION  195 

The  lead  pans  hold  the  following  temperatures: 

No.  1  about  320°F 
No.  2  about  330 
No.  3  about  360 
No.  4  about  345 
No.  5  about  330 

The  Kessler  apparatus  really  covers  two  steps  of  the  concen- 
trating field,  as  it  will  bring  chamber  acid  up  to  98  per  cent  H2SO4 
in  one  operation.  In  this  apparatus  hot  air  is  used  to  concentrate 
the  acid.  The  operation  requires  that  a  current  of  hot  air  shall 
be  brought  into  contact  with  the  liquid,  to  immediately  reduce 
its  temperature.  The  air  must  become  thoroughly  saturated 
with  steam  and  acid  vapor.  The  apparatus  must  be  so  con- 
structed that  it  will  stand  the  action  of  hot  acid,  and  that  the 
deposits  do  not  give  any  trouble.  Under  these  conditions  the 
acid  may  be  concentrated  at  a  temperature  far  below  its  boiling 
point,  for  instance,  to  concentrate  acid  to  95  per  cent  H2SO4, 
boiling  at  280°C.,  the  temperature  needs  to  be  only  180°  to  190°C. 

The  part  of  the  apparatus  where  the  gases  are  saturated  with 
acid  vapors,  and  the  temperature  greatly  reduced,  is  called  the 
" saturator. "  Immediately  above  it  is  placed  the  "recuperator, " 
where  the  acid  vapors  are  caught.  This  recuperator  resembles 
the  dephlegmating  columns  used  in  the  rectification  of  spirits. 

The  saturator  is  a  trough  built  of  acid-proof  slabs,  surrounded 
by  a  thick  lead  jacket,  both  of  which  must  resist  hot  acid  and 
gases.  Between  the  bottom  and  cover  of  the  saturator  there  are 
placed  several  partitions,  to  force  the  hot  gases  into  immediate 
contact  with  the  acid.  In  this  way  the  gases  are  quickly  reduced 
to  150°C.,  and  the  acid  as  quickly  gives  off  its  water  and  some 
acid  vapor.  The  acid  is  run  off  from  the  saturator  in  the  con- 
centrated state,  at  the  end  furthest  from  the  fire  box. 

The  recuperator  consists  of  a  tower,  lined  with  acid-proof 
brick,  and  containing  5  horizontal  plates,  dividing  the  tower  up 
into  6  equal  parts;  each  plate,  however,  is  perforated  by  100  holes 
with  raised  edges,  so  that  there  is  always  a  film  of  acid  on  the 
plates.  The  holes  are  covered  by  inverted  porcelain  cups  with 
jagged  edges,  forming  an  hydraulic  seal,  so  that  ascending  gases 
must  bubble  up  through  the  acid  on  the  plates.  The  chamber 
acid  runs  to  the  top  plate  first,  and  then  by  overflow  piping  to  the 
other  lower  ones,  and  finally  to  the  saturator.  The  gases  from 


196  AMERICAN  SULPHURIC  ACID  PRACTICE 

the  saturator  are  drawn  up  through  the  holes,  and  so  through  the 
descending  acid,  by  an  injector,  and  SO3  is  absorbed,  and  a  little 
water  given  up,  as  in  the  tower  of  the  just  described  heat 
exchanger. 

A  thermometer  is  placed  at  both  top  and  bottom  of  the  recu- 
perator, for  temperature  control.  The  lower  one  should  stand 
at  300°F.,  the  upper  a  little  under  200°F. 

After  leaving  the  recuperator  the  gases  pass  through  a  coke 
tower,  to  recover  any  acid  spray. 

Ninety-eight  per  cent  H2SO4  can  be  made  in  one  operation,  from 
chamber  acid.  Gas  firing  is  most  satisfactory,  and  requires  8 
per  cent  coke,  on  the  acid  concentrated.  The  injector  requires 
2  per  cent  steam,  also  figured  on  the  concentrate. 

The  Benker  system  is  a  third  modification  of  the  heat  ex- 
changer, all  being  based  upon  the  principle  of  the  Glover  Tower, 
although  I  do  not  know  who  first  applied  this  system  in  this  way. 
The  Benker  system  uses  a  cascade  instead  of  a  pan,  however,  for 
the  final  heating. 

Two  parallel  rows  of  duriron  or  tantiron  plates,  are  arranged 
in  cascade  form,  with  the  flue  running  up  between  the  two  rows. 
On  account  of  the  great  fire  space,  and  the  thin  film  of  acid, 
evaporation  is  very  rapid.  The  cascades  are  covered,  and  the 
gases  are  lead  to  a  packed  tower,  which  removes  the  SO3,  the 
draught  being  provided  by  a  fan.  A  cooling  box  is  necessary, 
between  the  cascades  and  the  tower,  as  the  gases,  owing  to  the 
intimate  contact  with  the  heat,  due  to  the  thin  film  of  acid,  are 
too  hot  for  good  working  of  the  tower.  The  gas  passes  through 
a  coke  tower  after  the  tower* 

The  acid  leaves  the  tower  at  the  bottom,  at  a  concentration  of 
61°  to  62°Be.,  and  a  temperature  of  300°F.,  running  direct  to  the 
cascades. 

Such  a  plant,  to  cost,  in  1916,  $3,500,  will  furnish  9  to  10  tons 
of  92  to  93  per  cent  H2S04,  clear  as  water,  in  24  hours,  with  a 
coke  (for  gas)  consumption  of  12  to  15  per  cent  on  the  acid  made. 
At  this  concentration  losses  will  run  about  3  per  cent,  and  higher 
on  98  per  cent  acid. 

Because  of  the  thin  film  of  acid  on  the  plates,  the  temperature 
of  the  acid  will  get  higher  than  in  either  of  the  two  previously 
mentioned  systems,  giving  this  method  greater  capacity,  but 
driving  off  more  SO3:  and  as  the  tower  acid  is  less  efficient,  the 
higher  the  S03  content  of  the  ascending  gases,  the  losses  are  consid- 


CONCENTRATION  197 

erably  greater.  Of  the  three,  the  writer  prefers  the  "heat 
exchanger." 

The  objection  to  the  use  of  direct  heat  in  all  concentrating 
systems  is  that  at  the  high  temperatures,  up  to  800°C.,  from  direct 
flame  there  is  considerable  dissociation  of  the  acid  into  H2O  and 
SO3,  requiring  very  large  spaces,  usually  coke  boxes,  to  give 
room  and  thus  time  to  assist  in  reassociation.  For  instance,  in 
a  Kessler  system,  concentrating  5  tons  of  66°Be.  acid  per  24  hours, 
a  coke  box  24  ft.  long,  8  ft.  wide  and  6  ft.  high  is  needed:  and  this 
coke  box,  with  its  supports,  constitutes  a  large  proportion  of  the 
cost  of  plant. 

The  Buffalo  Foundry  and  Machine  Co.  system  gets  away  from 
this  by  combining  outside  and  direct  heating,  as  follows: 

The  hot  gases  pass  from  the  fire  around  the  acid  pot  at  a 
temperature  of  approximately  800°C.;  thence  to  a  heat  exchanger, 
where  they  heat  air  that  is  under  5  Ib.  pressure  and  then  pass  into 
the  tee  that  is  at  the  bottom  of  the  concentrating  tower,  at  a  tem- 
perature of  approximately  300°C.  This  tower,  of  four  2-ft.  6-in. 
sections  of  cast  iron,  36  in.  in  diameter  inside  of  lining,  is  lined 
with  sheet  lead  and  acid-resisting  brick,  discharges  the  vapors, 
now  well  cooled  down,  through  a  12-in.  I.D.  lead  pipe,  to  a  6-ft.  X 
6-ft.  X  3-ft.  scrubber,  where  any  acid  carried  over  is  condensed. 
There  is  very  little  dissociation  at  the  temperatures  employed, 
and  this  small  scrubber,  is  ample  in  size. 

The  weak  acid  feed  is  to  the  heat  exchanger,  which  is  heated 
by  the  concentrated  acid,  hot  from  the  pot.  From  the  heat 
exchanger  the  weak  acid  goes  to  the  top  of  the  tower,  trickling 
down  over  the  tower  packing  meeting  the  ascending  gases  from 
the  tee,  and  runs  off  into  the  acid  pot.  The  final  concentration 
takes  place  in  this  pot,  and  the  overflow  from  it  is  66°Be*.  and  plus 
acid,  which  is  cooled  for  storage  by  heating  the  feed  acid. 

This  pot,  in  addition  to  its  acid  feed  from  the  tower,  receives 
the  heated  air  under  pressure,  from  the  heat  exchanger,  near  the 
bottom.  A  small  removable  liner  is  placed  to  receive  the  im- 
pingment  of  the  air  and  protects  the  pot.  A  collar  of  high-silicon 
iron,  carried  on  lugs,  and  outside  of  which  is  the  outlet,  pre- 
vents the  weaker  acid  from  reaching  and  attacking  the  pot  itself. 
The  arrows  in  the  sketch  show  the  course  of  the  acid  within 
the  pot. 

The  air  introduces  heat  and  agitation,  furnishing/  in  effect, 
"direct  flame,"  but  at  a  low  enough  temperature  to  avoid  acid 


198 


AMERICAN  SULPHURIC  ACID  PRACTICE 


Cooling  Pot  with 

Lead  Cooling  Coil  - — IT 


From  Weak  Acid  Tank 


FIG.  65. 


CONCENTRATION  199 

dissociation  and,  of  course  the  heat  outside  the  pot  is  similar 
to  that  applied  to  the  bottom  of  a  pan. 

The  vapors  rising  from  the  pot  pass  to  one  leg  of  the  tee,  the 
other  one  of  which  receives  the  gases  from  the  heat  exchanger, 
and  up  through  the  tower. 

The  same  number  of  heat  units  is  applied  as  sometimes  give  a 
dissociation  up  to  25  per  cent,  at  a  concentration  to  97.5  per  cent 
in  a  direct  heated  pan  system,  but  the  distribution  is  better. 

Tubes  and  small  castings  are  made  of  high-silicon  iron-larger 
ones,  such  as  the  pot  and  tower  sections,  are  close  grained 
semi-steel. 

This  system  uses  8  per  cent  to  10  per  cent  of  coke  on  the  acid 
made  depending  upon  the  strength  of  the  feed,  and  final  concen- 
tration of  the  acid. 

PLATINUM  STILLS 

The  concentration  of  sulphuric  acid  in  platinum  dishes  is  still 
carried  on  to  a  small  extent  in  this  country,  when  very  pure  acid 
is  required,  as  for  laboratory  use.  But  with  platinum  at  $145 
an  ounce  (1920),  the  contact  process  can  use  it  more  economically. 

In  the  platinum  still  of  today  only  the  pan  is  platinum,  the  bell 
being  a  lead  water  jacket.  The  size  of  the  still  depends  upon  the 
production — roughly  75  oz.  of  platinum  per  ton  of  95  per  cent  acid 
produced  per  24  hours.  A  dish  to  turn  out  seven  tons  of  95  per 
cent  acid  daily  would  weigh  45  lb.,  be  3J^  ft.  in  diameter,  and 
cost  $78,300.  The  rim  of  the  dish  has  a  groove  in  which  the  lead 
bell  sets  loosely,  condensation  forming  an  hydraulic  seal.  There 
is  an  overflow  pipe  from  this  seal,  to  remove  the  weak  acid 
condensed. 

A  large  pipe  runs  over  from  the  top  of  the  bell,  and  dips  down 
into  a  condenser,  through  which  the  vapors  pass,  the  weak 
condensate  from  here  and  the  seal  being  added  to  the  feed.  Two 
or  three  stills  make  up  a  set,  the  acid  from  the  first  one  going  by 
gravity  to  the  next,  for  further  concentration. 

The  still  is  carried  upon  a  cast-iron  frame. 

Acid  fed  to  platinum  stills  is  first  concentrated  in  bottom-fired 
lead  pans,  to  furnish  it  as  pure  and  clean  as  possible.  Glover 
tower  acid  contains  too  much  dissolved  iron  sulphate,  which 
settles  out  to  form  "crusts"  in  the  platinum  stills.  The  stills 
are  cleaned  by  running  them  as  nearly  dry  as  possible,  and  wash- 
ing them  out  with  hot  water  or  weak  acid,  which  dissolves  the 


200  AMERICAN  SULPHURIC  ACID  PRACTICE 

crusts.  The  frequency  of  cleaning  depends  entirely  upon 
the  acid  fed,  it  may  be  every  day,  it  may  be  every  three 
months. 

The  acid  is  kept  very  shallow  in  the  still,  from  2  to  3  in.  only, 
and  even  comparatively  small  heat  fluctuations  cause  large  varia- 
tions in  the  concentration  of  acid  produced.  Coal  firing  is  not 
sufficiently  steady,  so  gas,  usually  from  a  producer,  is  used,  and 
gives  excellent  results. 

The  lead  work  on  such  a  set  of  stills  has  to  be  renewed  in  two 
years.  The  platinum  is  also  slowly  dissolved,  losses  running 
from  .2  to  .3  g.  per  ton  of  98  per  cent  acid  made. 

VITREOSIL  CASCADE  CONCENTRATORS 

The  continuous  cascade  concentrator  was  originated  in  Eng- 
land, and  at  first  consisted  of  four  or  five  glass  retorts  arranged 
in  cascade  over  a  coal-  or  a  gas-fired  furnace.  Porcelain  dishes 
set  in  an  acid-proof  brick  chamber  were  later  substituted  for 
glass  retorts.  One  of  the  most  serious  drawbacks  to  this  system, 
whether  using  glass  or  porcelain,  was  the  heavy  breakage  of  the 
pans  and  the  difficulty  of  getting  high  fuel  efficiency;  hence  the 
system  was  not  generally  adopted. 

With  the  development  of  vitreosil  (fused  silica)  in  1906,  there 
was  a  more  general  adoption  of  the  use  of  cascade  systems,  and 
several  were  installed  in  this  country.  The  largest  is  at  the  plant 
of  the  Davison  Chemical  Co.,  at  Baltimore,  Md. 

Plant  for  full  range  of  concentration  (50°  to  66°Be.)  is  com- 
posed of  rectangular  trays  and  circular  basins.  The  trays  mea- 
sure 24  X  12  X  6  in.  and  are  used  only  in  the  operation  of  the 
plant  covering  the  range  from  50°  to  60°Be*.  This  portion  of  the 
plant  is  uncovered,  as  the  fume  from  acid  below  60°Be.  is  practi- 
cally acid  free.  The  basins  are  used  on  the  range  60°  to  66°Be. 
and  may  be  either  12  in.  or  16  in.  in  diameter.  This  portion  of 
the  plant  must  be  covered,  as  the  fumes  from  acid  of  higher 
strength  than  60°Be.  carry  sulphuric  acid  and  it  is  essential 
that  these  fumes  be  scrubbed  of  their  acid  content  before  allowing 
them  to  pass  out  into  the  air.  If  higher  strengths  than  66°Be. 
are  required,  the  acid  from  the  cascade  may  be  run  directly  into 
iron  pans,  which  would  be  so  set  up  as  to  be  fired  from  the  same 
firebox  as  the  basin  cascade,  and  the  fumes  from  this  acid  re- 
covered by  one  of  the  systems  previously  described. 


CONCENTRATION  201 

In  the  full  range  plant,  the  tray  and  basin  cascades  are  set 
up  so  as  to  allow  a  continuous  flow  from  one  to  the  other  and  to 
allow  a  fire  from  a  single  firebox. 

There  is  but  slight  loss  of  acid  in  the  concentration  up  to  66°Be., 
this  usually  amounting  to  about  2  per  cent,  based  on  the  weight 
of  finished  acid,  and  usually  running  in  strength  from  10°  to  12°Be. 
for  the  entire  distillate.  For  the  fuel  efficiency  of  the  cascade 
concentrator,  it  is  usual  practice  to  concentrate  over  the  range  60° 
to  66°Be.  with  a  fuel  consumption  of  about  14  per  cent,  while 
over  the  range  50°  to  66°Be*.,  the  fuel  consumption  is  usually 
about  17  per  cent.  The  above  percentage  figures  are  based  on 
the  weight  of  finished  acid  and  figuring  on  soft  coal  as  a  fuel 
running  about  13,000  B.T.U.  Breakage  in  usual  operation 
amounts  to  about  5  per  cent  on  the  basins  and  about  1  per  cent 
on  the  trays  per  annum. 

The  cascade  concentrator  is  applicable  to  the  concentration 
of  sulphuric  acid  from  either  a  brimstone  or  pyrites  set.  Sludge 
acid  may  be  recovered  in  the  cascade  plant  if  free  from  high  per- 
centages of  mineral  or  organic  matter,  which  will  cause  excessive 
frothing  due  to  evolution  of  SO2.  Sludge  acids  carrying  only 
small  amounts  of  organic  matter,  and  in  which  the  frothing  would 
not  be  excessive,  may  be  readily  carried  on  in  this  type  of  plant 
by  using  a  specially  designed  basin. 

The  cascade  type  of  concentrator,  using  vitreosil  dishes  is 
especially  recommended  where  freedom  from  contamination 
during  concentration  is  desired. 

Vitreosil  is  unaffected  by  sulphuric  acid  of  any  strength  or  at 
any  temperature.  Its  melting  point  is  about  1,750°C.,  although 
there  is  slight  softening  around  a  temperature  of  1,400°C.  Vit- 
reosil due  to  its  extremely  low  coefficient  of  expansion  .00000054 
per  degree  centigrade,  over  the  range  0°  to  1,000°C.,  about  Jf  7 
that  of  glass,  is  applicable  to  high  temperature  operations. 

The  process  of  the  Kalbperry  Corporation,  worked  out  from 
the  tower  developed  at  the  plants  of  the  Franklin  H.  Kalbfleisch 
Co.,  cannot  be  described,  as  it  is  a  trade  secret,  unpatented, 
licenses  being  issued  for  its  use.  One  important  feature  is  that 
it  will  give  a  high  degree  of  efficiency  on  concentrating  very 
dirty  acid,  the  concentrate  being  perfectly  clean.  Operating  cost 
is  low,  in  1916,  it  being  50  cts.  per  ton  of  97  per  cent  acid  pro- 
duced. Exclusive  of  building  and  license,  this  tower  cost,  in 
1916,  about  $4,000. 


202  AMERICAN  SULPHURIC  ACID  PRACTICE 

The  license  charge  is  a  flat  fee  of  $3,500,  in  return  for  which  the 
client  receives  complete  detail  working  drawings,  bills  of  material, 
flow  sheets,  and  can  obtain  the  service  of  a  skilled  operator  for 
a  time  to  demonstrate  and  put  the  tower  on  a  working  basis. 

RECOVERING  SULPHURIC  ACID  FROM  A  MIXTURE  WITH  NITRIC 

ACID 

Nitric  acid  alone  cannot  be  handled  in  steel  or  iron  containers, 
because  of  its  corrosive  action,  unless  it  is  sufficiently  dilute.  As 
in  most  nitrating  operations  water  is  liberated,  and  must  be 
cared  for,  sulphuric  acid  fulfills  the  double  function  of  diluting 
nitric  acid  to  a  point  where  it  will  not  attack  iron  containers  too 
energetically,  and  of  absorbing  the  water  liberated. 

It  is  impracticable  to  remove  this  water  without  separating 
the  two  acids  and  reconcentrating  them,  and  a  brief  description 
of  the  most  successful  method  of  separation  is  in  order. 

Nitric  acid  boils  at  188°F.,  water  at  212°F.,  but  a  mixture  below 
91  per  cent  acid  boils  at  a  higher  point  still.  68.5  per  cent  HN03 
boils  at  251.5°F.,  which  is  the  highest  boiling  point  of  nitric  acid 
of  any  concentration,  and  nitric  acid  of  any  concentration,  if 
boiled  alone,  will  approach  that  concentration,  by  the  loss  of 
HN03  if  above  that  concentration,  of  water  if  below  68.5  per 
cent.  It  will  then  evaporate  to  dryness,  remaining  at  •  68.5 
per  cent. 

So  it  is  necessary  to  use  something  to  retain  the  water,  letting 
the  HNO3  fumes  pass  to  the  condensers,  and  sulphuric  acid  is  an 
ideal  substance. 

A  tower  21  ft.  high,  3  ft.  in  diameter,  packed  with  quartz,  with 
openings  for  steam  at  the  bottom  and  for  the  concentrating 
mixture  at  the  top,  with  sulphuric  acid  opening  at  the  bottom  and 
•fume  (HN03),  outlet  at  the  top,  is  the  apparatus  required. 

The  concentratng  mixture,  strong  H2S04  and  weak  HNO3,  is 

,    .      ,  f  per  cent  H2SO4  ~ 

derived  from  the  formula ,  ^  ari — r~  .  TJXT^   =  S 

per  cent  H2SO4  -f  per  cent  HNO3 

H  =  per  cent  HN03  in  mixture, 
h  =  per  cent  H2SO4  in  mixture, 

100H 
then,  =  100  -h 

S  is  therefore  directly  proportional  to  H2S04,  and  inversely 
proportional  to  H2O,  and  is  a  direct  measure  of  the  heat-develop- 


CONCENTRATION  203 

'  . 

ing  capacity  of  the  mixture :  and  since  a  definite  amount  of  HNO3 
requires  a  definite  amount  of  heat  to  volatilize  it,  it  must  be  high 
for  high  HNO3,  low  for  low. 

With  H2S04  about  84  per  cent  the  mixture  automatically  falls 
about  right  for  complete  denitration. 

The  addition  of  water,  in  the  form  of  steam,  is  the  one  weak 
point.  It  takes  about  a  pound  of  steam  to  distill  a  pound  of 
HN03. 

The  concentrating  mixture  is  fed  in  at  the  top  and  trickles  down 
over  the  quartz,  meeting  the  steam  blowing  in  at  the  bottom. 
The  heat  from  the  steam,  and  that  from  its  reaction  with  the 
H2SO4,  volatilize  all  the  HNO3,  which  rises,  being  pulled  through 
by  suction. 

As  it  approaches  the  top  the  steam  begins  to  condense,  and 
having  greater  affinity  for  the  H2S04  than  for  the  HNO3,  unites 
with  it,  leaving  the  vapors  practically  water  free.  The  reverse 
of  this  process  takes  place  in  the  decending  mixtures,  more  and 
more  HNOs  is  driven  off  in  its  downward  passage,  until  at  the 
bottom  there  is  no  HNOs,  the  mixture  being  only  H2SO4  and 
H2O.  A  top  temperature  of  under  200°F,  is  excellent  operation, 
and  that  at  the  bottom  should  run  300  to  330°F. 

The  rate  of  feed  mixture  and  steam  must  be  correct,  or  imme- 
diate trouble  insues.  Too  little  mixture  means  too  little  H2SO4 
to  unite  with  the  steam,  the  excess  of  which  escapes  at  the  top, 
raising  the  top  temperature,  and  giving  weak  nitric  acid.  Also, 
too  much  steam  may  first  liberate,  and  then  condense  and 
reabsorb  HNO3. 

If  too  much  concentrating  mixture  is  used,  there  will  not  be 
heat  enough  to  vaporize  all  the  HNO3. 

The  weak  sulphuric  acid  is  then  concentrated  in  lead  and  iron 
pans  and  the  heat  exchanger,  up  to  66°Be. 

The  vapors  from  the  concentrating  towers  are  almost  entirely 
HN03,  with  a  little  H2O,  NO  and  N02,  and  traces  of  N2,  N2O, 
and  CO2.  All  the  water,  and  practically  all  the  HNOs,  are  con- 
densed, a  little  HN03  going  over  as  a  spray  into  the  absorbtion 
towers,  where  it  condenses.  The  NO  is  oxidized  to  N02  by  the 
air  present;  and  then  reacts  as  follows  with  water : 

2N02  +  H20  =  HNOs  +  HN02 

The  HNO3  is  absorbed,  and  the  HNO2  reacts  as  follows: 
3HN02  =  2NO  +  H20  +  HNO3, 


204  AMERICAN  SULPHURIC  ACID  PRACTICE 

the  NO  being  oxidized  and  the  product  decomposed  over  and 
over  again,  until  it  is  practically  all  acid. 

Spent  acids  from  the  nitration  of  nitro-cellulose,  nitro-glycerine, 
or  similar  substances  contain  so  small  an  amount  of  low  oxides 
of  Nitrogen  actually  in  chemical  combination  with  H2S04,  that 
whilst  dilution  of  the  spent  acid  in  the  denitrating  tower  is  neces- 
sary, such  dilution  need  not  be  carried  to  anything  like  the  extent 
that  is  necessary  when  handling  spent  acid  from  nitration  of 
hydrocarbons:  and  in  the  case  of  spent  acid  from  glycerine  it 
may  be  regarded  as  more  of  a  distilling  process  than  dinitration; 
the  principal  function  of  the  tower  in  this  case  (nitro-glycerine) 
is  to  remove  the  nitric  acid  as  such  from  S/A  in  a  most  highly 
concentrated  state,  and  decompose  traces  of  N.G.  in  S/A. 

But  ''spent"  from  the  nitration  of  hydrocarbons,  in  the  manu- 
facture of  T.N.T.,  picric  acid,  etc.,  usually  contains  about  2  per 
cent  nitric  acid  and  4  per  cent  of  the  lower  oxides :  in  the  case  of 
one  large  T.N.T.  plant  in  Canada  it  was  the  equivalent  of  7  per 
cent  of  100  per  cent  HNOs — certainly  well  worth  recovering. 

These  lower  oxides  are  in  large  part  not  free,  but  are  combined 
as  definite  compounds  with  sulphuric  acid,  and  the  Buffalo 
Foundry  &  Machine  Co.  has  worked  out  a  plant  which  will 
make  a  98  per  cent  recovery  at  low  cost. 

Their  process  for  handling  S/A  from  nitro-glycerine  or  nitro- 
cellulose is  based  upon  careful  heat  control:  and  this  includes  the 
superheating  of  the  steam  introduced,  furnishing  the  amount  of 
heat  required  with  the  minimum  of  water,  thus  keeping  down  the 
amount  of  water  which  must  be  removed  by,  and  later  from,  the 
sulphuric  acid. 

A  12-in.  column  of  high  silicon  metal  lagged  with  4  in.  of 
asbestos,  or  acid  proof  lined  C.I.,  35  ft.  high,  is  fed  at  the  top  with 
heated  acid,  the  temperature  being  controlled  within  approxi- 
mately 1°C.,  automatically.  This  top  temperature  is  kept  under 
100°C.,  the  exact  point  depending  upon  local  conditions  (Fig.  66). 

If  it  is  at  100°C.,  the  recovery  will  be  in  93%  HN03 
If  it  is  at    95°C.,  the  recovery  will  be  in  97%  HN03 

The  steam,  carrying  100°  of  super-heat,  is  introduced  through 
high-silicon  iron  tubes,  full  of  small  holes,  6  in.  below  the  surface 
of  the  liquid  in  the  bottom.  The  bottom  temperature  is  main- 
tained at  approximately  300°C.  The  amount  of  steam  intro- 
duced being  kept  down,  the  H2SO4,  absolutely  denitrated,  runs 


CONCENTRATION 


205 


out  78  per  cent-80  per  cent,  instead  of  the  customary  60  per  cent 
that  obtains  from  the  ordinary  denitrating  system.  At  this 
strength  iron  pans  may  be  used  for  concentrating,  eliminating 
lead  pans  entirely. 

The  fume  leaves  the  tower  at  the  top,  and  is  carried  down 
through  a  condenser,  from  which  the  condensate  flows  to  a  re- 
ceiver. From  this  receiver  the  non-condensible  gases  are  sucked 
through  oxidizing  towers,  in  series,  similar  in  construction  to  the 
denitrating  tower,  but  of  greater  diameter  and  less  height.  In 
these  towers  good  construction,  low  velocity,  plenty  of  air,  and 


••TEMPERATURE  CONTIfOlLER 


FIG.  66. 

good  atomizing  of  the  absorber  make  the  oxidation  good  enough 
to  make  a  98  per  cent  recovery. 

The  absorbing  liquid  fed  to  each  tower  is  from  the  base  of  the 
succeeding  tower,  raised  to  a  receiving  tank  above  the  tower,  and 
fed  through  an  atomizer,  with  valve  control.  The  fume  is  fed 
at  the  bottom  of  each  tower,  and  drawn  off  at  the  top. 

Mr  Authur  Hough,  the  designer  of  the  apparatus,  stated  that 
the  increased  operating  efficiency  of  a  modern  dynamite  plant,  of 
10  tons  per  day  capacity,  using  the  improved  acid  recovery 
system,  amounts  to  many  thousands  of  dollars  per  year. 

Corrosive  liquids,  like  strong  mineral  acids,  cannot  be  handled 
by  pumps,  so  the  pulsometer  has  been  developed.  It  is  shown 
in  section  in  Fig.  64;  is  made  of  chemical  stone  ware,  and  operates 


206  AMERICAN  SULPHURIC  ACID  PRACTICE 

as  follows:  Up  from  the  three  openings  shown  lead  tubes,  not 
over  an  inch  and  a  quarter  in  diameter.  The  inlet,  indicated  by 
"acid"  comes  from  a  raised  supply,  which,  flowing  in,  of  course 
rises  to  an  equal  height  in  the  two  other  tubes.  Sufficient  pres- 
sure of  air  is  then  blown  in  at  the  appropriate  opening,  to  over- 
come the  head  of  liquid.  This  air  blows  all  the  liquid  out  of  the 
air  inlet,  blows  down  and  under  the  partition,  and  of  course  rises 
through  the  liquid,  up  through  the  "out"  tube.  It  is  kept  from 
entering  the  incoming  tube  by  that  tube  being  extended  near  to 
the  bottom  of  the  pulsometer  than  the  bottom  of  the  partition. 

The  air,  rising  through  the  outgoing  tube,  carries  up  with  it 
bubbles  and  regular  "  slugs  "  of  liquid,  these  slugs  being  sometimes 
two  inches  thick.  If  the  tubes  are  too  large  in  diameter  the  slugs 
will  not  form,  the  air  just  blowing  up  through,  and  agitating  the 
liquid. 

The  heighth  to  which  a  liquid  can  be  raised  by  this  apparatus 
depends  upon  the  hydrostatic  head  of  the  entering  liquid,  air 
pressure,  diameter  of  tubes,  and  liquid  itself — nitric  acid  can  be 
raised  to  four  times  the  hydrostatic  head. 

BATTERY  ACID 

Battery  acid  is  pure  sulphuric  acid,  from  1.118  sp.  g.  to  1.125 
sp.  g. 

As  the  fume  from  the  concentration  of  acid  from  60°  to  66°Be\ 
runs  about  1.1  sp.  g.,  and  is  usually  clean,  and  of  good  purity,  it 
is  an  easy  matter  to  condense  this  fume,  and  concentrate  it,  using 
Vitreosil,  as  platinum  is  not  necessary  for  this  work. 


CHAPTER  XVII 
OUTLINE  OF  THE  CONTACT  PROCESS 

The  "Contact  Process"  takes  its  name  from  the  fact  upon 
which  it  depends — that  S0%  and  0  will  combine  to  form  SO3, 
under  proper  conditions  of  temperature,  concentration,  and 
purity  of  gas,  In  Contact  With  Platinum. 

Catalytic  action  has  been  known  since  1834,  when  Mitsherlich 
concluded  that  the  formation  of  ethyl  ether  and  water  from 
ethyl  alcohol,  in  the  presence  of  sulphuric  acid  did  not  depend 
upon  the  dehydrating  power  of  the  acid,  nor  upon  any  inter- 
mediate product  being  formed,  but  that  the  mere  presence  of 
the  acid  facilitated  the  reaction,  although  it  did  not  in  any  way 
enter  into  it. 

Mitsherlich  suggested  calling  this  contact  action,  but  the 
next  year  Berzilius  called  it  catalysis,  and  the  latter  name, 
while  certainly  no  better  nor  more  descriptive,  is  the  better 
known. 

SCOPE 

While  from  its  great  affinity  for  sulphur  tri-oxide,  water 
would  seem  the  logical  "absorber"  in  this  process,  thus  rendering 
possible  by  this  one  method  the  production  of  any  and  all  degrees 
of  concentration,  with  practically  no  change  of  apparatus  for 
different  concentrations,  from  the  very  weakest  to  100  per  cent 
80s,  we  are  practically  limited  to  the  making  of  fuming  acid, 
because  water  will  not  do. 

When  80s  comes  into  contact  with  water  vapor  a  white  mist 
is  formed.  As  to  its  character,  two  opposing  views  are  held. 
One  is  that  it  is  minute  drops  of  H2S04,  the  other  is  that  in  the 
presence  of  the  water  vapor  a  double  molecule,  820  e,  is  formed, 
and  that  this  molecule  is  not  easily  absorbed. 

Whatever  the  actual  reason  for,  or  character  of,  this  mist, 
it  resists  all  attempts  to  condense  it,  passing  through  as  many 
as  six  scrubbers,  with  sulphuric  acid  as  the  scrubbing  agent. 
It  is,  however,  partly  removed  by  condensation,  when  filtered 
through  fine  coke  or  asbestos  fibre.  It  causes  trouble  when 
present  before  the  conversion  by  its  activity  as  an  arsenic  or 

207 


208 


AMERICAN  SULPHURIC  ACID  PRACTICE 


lead  carrier,  and  in  the  absorber  house,  because  it  passes,  in 
apparently  undiminished  volume,  right  through  the  absorbers 
and  out  of  the  fume  stacks,  simply  throwing  away  that  much 
good  S03. 

This  mist  is,  of  course,  what  limits  our  product. 

Sulphuric  acid  of  98.3  per  cent  concentration,  or  more,  holds 
very  firmly  to  its  small  percentage  of  water,  but  as  concentration 
drops  below  that  point  the  space  above  the  acid  contains  water 
vapor,  and  especially  where  the  temperatures  are  at  all  high, 
as  in  the  first  scrubber  or  absorber  tower. 

So  we  are  in  practice  limited  to  sulphuric  acid  of  not  less  than 
98.3  per  cent  concentration  as  an  absorbing  medium,  which  in 
turn  means  that  we  must  make  an  acid  of  higher  concentration 
than  that:  in  other  words,  "fuming."  For  this  reason  the 
hopes  of  the  pioneers  in  the  industry,  that  this  process,  requiring 
a  smaller,  more  compact  plant,  would  ultimately  entirely  super- 
cede  the  older  process,  have  not  been  realized.  It  has,  however, 
entirely  eliminated  the  Starck  process  of  distillation  of  Bohemian 
shales,  and  the  "cracking"  of  sulphuric  acid  into  SO3  and  H2O, 
the  sulphur  tri-oxide  being  absorbed  as  in  our  process. 

TECHNOLOGY 

There  are  three  steps  in  the  production  of  sulphuric  acid  by 
the  contact  process. 


---f < 

Converters -— >K- -Absorbers 

FIG.  67. — Layout  for  contact  plant. 

(a)  Production  of  SO2  from  some  sulphur  bearing  material, 
as  pyrites  or  brimstone.  (While  this  process  has  not  yet  been 
adapted  to  the  utilization  of  metallurgical  gases,  as  the  Anaconda 
Company,  for  instance,  is  doing  with  the  chamber  process,  the 


OUTLINE  OF  THE  CONTACT  PROCESS  209 

Davison  Chemical  Co.  silica  gel  promises  great  things  in  this 
direction.) 

(b)  Oxidation  of  the  S02  to  SO3. 

(c)  Absorbtion  of  the  SO3  formed  by  a  weaker  acid,  until  the 
desired  concentration  is  reached. 

There  are  two  processes  used  extensively  in  this  .country,  the 
Badische,  the  rights  for  which  are  controlled  by  the  General 
Chemical  Co.,  and  the  Schroder-Grillo,  controlled  by  the  New 
Jersey  Zinc  Co.  The  methods  of  cooling  the  burner  gas,  the 
contact  mass,  and  the  means  of  bringing  the  purified  gas  up  to 
the  temperature  necessary  for  conversion  are  fundamentally 
different  in  the  two  processes. 

But  they  are  alike  in  that  both  require  a  clean  gas  for  the 
conversion  of  SO2  into  SO3,  and  that  the  same  underlying 
principles  control  their  absorbtion  systems. 

The  production  of  SO2  has  already  been  covered  in  Chapter  V, 
the  methods  in  use  being  common  to  both  the  chamber  and 
contact  processes.  After  this  the  gas  must  be 

Cooled; 

Freed  from  dust,  moisture,  small  quantities  of  SO3  formed  in 
the  burners,  and  other  impurities; 
*    Freed  from  any  mechanically  carried  sulphuric  acid; 

Filtered  to  remove  any  last  traces  of  liquids,  which  at  this 
point  is  usually  a  sulphuric  acid  mist; 

Heated  to  the  conversion  temperature; 

Converted ; 

Cooled; 

Absorbed; 

The  acid  weighed  and  delivered. 

Lunge  says,  ironically,  in  his  " Sulphuric  Acid  and  Alkali:" 
"  There  are  279  sulphuric  acid  plants  in  the  United  States  today, 
of  which  44  employ  chemists."  Working  within  the  compara- 
tively narrow  limits  that  we  must  in  this  process,  a  well  equipped 
laboratory  is  a  necessity — even  more  than  in  the  chamber 
process — for  this  must  be  controlled  all  the  way  through  by 
analysis.  If  the  acid  in  either  the  scrubbers  or  absorbers  gets 
too  low  in  concentration  we  will  soon  be  face  to  face  with  a  badly 
corroded  system;  if  the  absorber  acid  gets  too  high,  its  absorbing 
properties  fall  off  very  fast,  and  we  loose  SO3  out  of  the  stacks. 
Acid  is  bought  and  sold  on  analysis,  both  as  to  concentration  and 
purity. 

14 


210 


AMERICAN  SULPHURIC  ACID  PRACTICE 


The  "strength"  of  the  gas  is  determined  at  regular  (every 
two-hour)  intervals,  by  the  Reich  starch-iodine  test:  it  is  most 
important  that  this  test  be  made  frequently  and  regularly, 
because  in  a  well  conducted  plant  the  loss  due  to  imperfect 
conversion  is  the  largest  loss,  and  the  gas  strengths,  both  relative 
and  absolute,  give  us  all  our  information  upon  this  important 
point. 

The  method  used  is  that  of  Reich  for  the  estimation  of 
sulphurous  acid  in  gas,  and  while  of  no  higher  degree  of  accuracy 
than  any  other  color  test,  is  sufficiently  accurate  to  control  the 


FIG.  68. 

process.  This  test,  and  the  pyrometers  for  reading  the  converter 
temperatures  are  our  only  guides,  but  with  a  properly  made  mass 
and  clean  gas,  are  enough  to  insure  a  satisfactory  conversion. 

This  is  of  course  occasionally  checked  by  the  laboratory, 
using  the  K2CO3  method. 

The  early  investigators  worked  along  serenely  at  this  process 
in  the  belief  that  SO2  and  O  must  be  present  in  stoichometrical 
proportions,  and  many  believed  that  nitrogen  had  a  distinctly 
bad  effect,  aside  from  its  diluting  the  gas;  which  means,  of 
course,  more  gas  to  move,  heat,  and  cool.  Those  who  were 


OUTLINE  OF  THE  CONTACT  PROCESS  211 

working  to  put  it  upon  a  commercial  basis,  and  saw  in  the  air 
the  natural  supply  of  oxygen,  tried  to  get  a  burner  gas  that  ran 
20.3  per  cent  SO2,  which  left  just  enough  oxygen  to  oxidize  the 
SO2  to  SO3.  But  the  rate  of  conversion  was  low;  the  process 
would  not  become  a  success. 

In  1878  Winkler,  realizing  that  reactions  do  not  go  to  con^ 
elusion  but  rather  to  a  state  of  equilibrium,  showed  that  there 
must  be  an  excess  of  air  to  get  a  good  rate  of  conversion,  and 
while  he  never  reached  100  per  cent  efficiency,  he  frequently  was 
able  to  get  up  to  99  per  cent.  This  is  high  for  general  practice, 
as  the  production  suffers  when  conditions  that  will  allow  so 
high  a  conversion  are  maintained. 

This  discovery  of  Winkler's  put  the  contact  process  upon  a 
commercial  basis. 

Suppose  that  the  plant  is  burning  1,000  Ib.  of  sulphur  an  hour, 
with  an  8  per  cent  entrance  gas.  If  the  SO2  content  is  increased 
to  9  per  cent  the  amount  of  sulphur  must  be  1,130  Ib.  per  hour 
and  correspondingly  more  acid  made,  without  any  increase  of 
expense  except  in  the  one  item  of  raw  material-less  than  50  per 
cent  of  the  cost  anyway.  The  same  labor  and  overhead  pay  for 
the  increased  production. 

Acid  production  may  be  figured  as  follows: 

Let  a  =  available  SO3  =  sulphur  burned  X  2.5  X  per  cent  yield, 

b  =  pounds  water  made  per  1,000  Ib.  fuming  acid, 

x  =  weight  of  weak  acid  used  per  day, 

y  =  weight  of  fuming  acid  produced  per  day, 

c  =  per  cent  strength  of  weak  acid, 

d  =  per  cent  strength  of  fuming  acid, 
Then 

v-    ^  1000  (a  +  s) 

^"1000^  1000-6 

and 


But  as  the  S(>2  content  of  the  gas  goes  up,  above  a  certain 
point,  the  rate  of  conversion  goes  down.  This  point  is  not  the 
same  for  all  plants,  nor  is  it  a  constant  for  any  one  plant,  varying 
with  the  contact  mass  and  the  purity  of  the  gas,  which  in  itself 
varies  with  the  weather,  etc.  Seven  per  cent  may  be  taken  as  a 
safe  starting  point,  however,  and  the  best  working  conditions  for 
the  individual  plant  then  determined.  It  is  impossible  to  draw  a 
curve  showing  per  cent  conversion  plotted  against  per  cent  SOa 


212  AMERICAN  SULPHURIC  ACID  PRACTICE 

in  the  gas — and  it  is  equally  impossible  to  show,  except  for  the 
individual  plant,  at  what  point  the  decreased  conversion  ceases 
to  be  overbalanced  by  the  increased  production. 

Gases  leave  the  converters  around  350°C.;  much  too  hot  to 
make  possible  any  high  degree  of  absorbtion,  which  should  be 
conducted  not  far  from  40°C.  (104°F.).  The  methods  of  remov- 
ing this  heat  used  by  the  Badische  and  the  Schroder  processes 
are  fundamentally  different — the  former  uses  it  to  heat  the  incom- 
ing gases,  the  latter  wastes  it  by  radiation.  The  net  result  is  a 
gas  of  the  proper  temperature,  which  is  brought  into  intimate 
contact  with  sulphuric  acid,  not  less  than  98.3  per  cent,  by  towers 
and  tanks,  such  as  are  described  in  the  chapter  on  absorbtion, 
the  SOa  absorbed,  and  the  remaining  gases  passed  out  through 
.the  stack.  This  remainder  consists  of  N,  O,  the  minor  gases 
contained  in  the  air,  and  practically  all  the  unconverted  S02 
— this  latter  constituting  by  far  the  greater  part  of  the  loss  in 
the  system.  The  S(>2  absorbed  by  the  acid,  either  in  the  scrub- 
bers or  absorbers,  and  slowly  oxidized  to  S03,  thus  becoming  part 
of  the  acid,  is  not  only  inconsiderable,  but  is  not  a  loss. 

The  degree  of  concentration  of  the  finished  product  must 
depend  upon  the  market  to  which  it  goes.  Higher  acid  is  made 
more  slowly,  as  the  absorbing  power  of  any  acid  varies  directly 
as  its  vapor  pressure,  and  reference  to  the  curve  of  vapor  pres- 
sures in  Chapter  XXIII  will  show  the  very  rapid  increase  in 
vapor  pressure  with  concentration,  of  " fuming."  While  acid 
of  80.5  per  cent  SO3  will  absorb  practically  100  per  cent  of  the 
SO3  in  any  gas  passed  through  it,  at  88  per  cent  S03  it  will  only 
take  up  23  per  cent. 

The  freezing  point  must  be  considered  very  carefully  in  decid- 
ing what  concentration  of  acid  to  make.  A  glance  of  the  curve 
of  freezing  points,  Chapter  XXIII,  shows  a  wide  range  of  choice. 
Eighty-four  and  five  tenth  per  cent  SO3  will  remain  liquid  at 
the  lowest  temperature  of  any  really  concentrated  acid.  The 
addition  of  a  few  per  cent  of  nitric  acid  drops  the  freezing  point 
many  degrees,  but  spoils  the  acid  for  some  purposes. 

COSTS 

A  thousand  pounds  of  100  per  cent  sulphuric  acid  made  by  the 
contact  process  cost,  in  1914,  from  $7.50  to  $8.50.  A  plant  to 
burn  1000  Ib.  of  brimstone  an  hour  cost  then  $150,000.  This 


OUTLINE  OF  THE  CONTACT  PROCESS  213 

does  not  include  power  house,  sulphur  storage,  shops,  office, 
laboratory,  or  any  auxiliary  buildings.  Operating  labor  will 
be  \y±  to  IJ-^  man  hours  per  1000  Ib.  acid.  Capital  expense 
must  of  course  be  figured  for  each  case. 

Where  depreciation  leaves  off  and  maintenance  begins  is  a 
difficult  question  to  answer.  The  usual  practice  is  to  take  a  figure 
gained  by  experience  for  depreciation,  and  all  renewals  above 
that  are  charged  to  maintenance.  Maintenance  will  vary  so  with 
the  management  that  it  is  not  possible  to  give  any  figure  that 
could  serve  as  a  guide. 

An  industry  handling  corrosive  material  expects  very  rapid 
depreciation.  Weak  sulphuric  acid,  and  nitric  acid,  even  in  small 
quantities,  destroy  iron  and  steel  very  rapidly.  The  usual 
method  of  handling  sulphuric  acid,  by  compressed  air,  puts 
serious  strains  upon  parts  of  the  apparatus.  When  acid  mixtures 
are  made  a  great  deal  of  heat  is  evolved  and  high  temperatures 
result,  producing  expansion  that  will  have  serious  results  unless 
the  design  of  the  plant  provides  for  expansion  bends  as  liberally 
as  on  steam  lines.  Expansion  joints  are  not  practicable  for  pipe 
work  to  handle  corrosive  liquors. 

Fuming  sulphuric  acid  does  not  destroy  cast  iron  by  dissolving 
it,  but  by  bursting.  Cracks  appear,  in  no  particular  direction, 
and  sometimes  the  fitting  actually  suddenly  explodes  with  a 
considerable  report.  Examination  of  the  broken  pieces  rarely 
shows  a  flaw.  Dr.  Kneitsch  suggests  that  the  acid  enters  into 
the  pores  of  the  iron  and  becomes  vaporized,  producing  sufficient 
pressure  to  burst  it.  At  any  rate,  steel  castings  are  far  less 
liable  to  rupture,  and  as  the  pores  are  smaller  would  seem  to 
bear  out  this  theory. 

Acid  is  moved  by  "blow  cases" — horizontal  air  tight  tanks  of 
steel — with  the  acid  outlet  pipe  running  down  almost  to  the  bot- 
tom of  the  tank.  When  air  pressure  is  put  on  the  tank  the  acid 
rises  in  the  pipe,  and  is  thus  forced  around  without  the  use  of 
pumps,  upon  which  acid  is  very  hard. 

All  iron  gate  valves  should  be  used.  The  writer  prefers  sheet 
asbestos  packing,  although  sheet  lead  is  widely  used;  this  is  open 
to  two  objections — the  direct  action  of  the  acid  upon  lead,  and 
the  additional  corrosive  effect  of  the  electrolytic  action,  between 
two  metals,  in  the  presence  of  an  acid.  Brass  valves  have  a  very 
short  life  where  there  are  any  acid  fumes  in  the  air,  in  spite  of 
which  they  are  frequently  used  on  air  lines.  Any  valve  that  is 


214  AMERICAN  SULPHURIC  ACID  PRACTICE 

exposed  to  sulphuric  acid  and  is  not  frequently  eased  by  opening 
and  closing  will  soon  become  useless. 

The  use  of  rising  spindle  valves  is  not  to  be  thought  of.  A 
valve  left  open  by  mistake  can  be  attended  with  very  serious 
consequences,  and  the  only  safe  way  is  to  try  each  valve  each 
time:  any  type  of  valve  that  indicates  whether  it  is  open  or  shut 
without  actual  trial  tends  to  promote  carelessness  in  this  respect. 

Shower  baths,  where  the  full  stream  is  released  by  one  turn  of 
the  handle,  frequently  inspected,  should  be  placed  at  convenient 
intervals.  When  a  man  gets  any  acid  on  himself  he  wants  water, 
and  he  wants  it  in  a  hurry. 

The  first  aid  boxes  should  contain  a  bottle  of  a  solution  of  bi- 
carbonate of  soda,  boracic  acid,  an  eye  cup,  vasoline,  absorbent 
cotton,  and  surgical  tape.  This  will  care  for  any  probable  injury 
until  medical  aid  can  arrive. 

LABOR 

Such  a  plant  requires  on  each  shift  a  foreman,  burner  man, 
engineer,  fireman,  and  absorber-house  man,  who  also  attends  to 
the  scrubbers.  Three  men,  a  millwright,  a  pipe  fitter,  and  an 
electrician,  can  attend  to  all  maintenance,  and  the  outside  help, 
unskilled  labor,  will  bring  in  sulphur  or  ore,  coal,  pack  filters, 
remove  ashes  and  cinder,  help  the  maintenance  crew,  and  keep 
the  outside  clean.  The  size  of  this  crew  depends  upon  local 
conditions. 

The  operation  of  a  well-designed  contact  plant  is  easy  and 
pleasant,  and  it  is  always  possible  to  get  a  good  grade  of  labor. 
The  writer  prefers  Americans,  and  likes  them  young  enough  to 
be  easily  trained. 

In  any  continuous  process  cooperation  between  the  shifts  is  an 
absolute  essential.  Rivalry  is  to  be  discouraged,  as  it  tends  to- 
wards evils  such  as  trying  to  burn  more  sulphur  on  one  shift  than 
the  condition  of  the  burners  warrant,  leaving  the  following  shift 
to  pull  the  plant  out  of  the  hole.  Try  above  everything  else  to 
make  the  men  realize  that  the  DAY,  not  the  SHIFT,  is  the  unit 
of  time,  and  that  to  gain  an  apparent  temporary  advantage,  such 
as  the  burning  of  a  couple  of  thousand  pounds  more  sulphur  than 
the  shift  before,  and  leaving  the  plant  in  such  condition  that  the 
following  shift  cannot  come  within  four  thousand  pounds  of  the 
required  amount,  is  not  a  victory  at  all.  Have  a  meeting  that 
all  three  foremen  MUST  attend,  every  week.  Post  your  monthly 


OUTLINE  OF  THE  CONTACT  PROCESS  215 

yields  on  a  plant  bulletin  board.  Let  all  the  men  know  what 
the  results  are.  Success  of  all  kinds  appeals  to  all  men,  and  when 
the  figures  are  posted  the  men  will  forget  all  about  the  Athletics 
or  the  White  Sox,  while  they  digest — and  more  important,  dis- 
cuss— the  comparisons.  Where  there  are  few  men  employed 
they  come  to  know  each  other  well,  and  as  friends  will  get  along 
better  together  than  enemies,  an  unpopular  man  has  no  place 
in  such  an  organization. 

SHUTDOWN 

/ ' 

Because  of  the  corrosive  effect  of  sulphuric  acid  upon  iron,  a 
plant  making  or  handling  it  must  be  very  carefully  prepared  for 
a  shutdown,  either  temporary  or  permanent.  If  the  work  is 
done  as  outlined  below  the  plant  will  be  in  good  condition  to 
start  up  at  any  time  on  short  notice,  and  at  small  expense. 

It  is  a  good  plan  to  start  in  at  the  burners  and  work  through,  as 
in  this  way  nothing  is  likely  to  be  overlooked. 

All  traces  of  sulphur  must  be  burned,  the  burners  thoroughly 
cleaned,  and  then  painted,  inside  and  out.  The  outlook  will 
dictate  the  extent  of  repairs  and  replacements  of  arms,  etc.  All 
bearings  must  be  well  greased. 

Get  the  preheaters  going,  and  run  the  blowers  for  several  hours, 
thus  forcing  hot  air  through  the  converters  and  absorbers,  which 
will  remove  most  of  the  SO3. 

All  gas  lines  must  be  washed  out  thoroughly  with  a  little  soda 
ash  and  water,  then  rinsed  out  with  water  and  allowed  to  dry, 
and  then  blanked  off  into  convenient  sections,  the  blanks  being 
air  tight.  Fittings  at  low  points  in  the  lines  must  be  removed, 
putting  on  the  blanks  there. 

Pump  tanks  are  filled  up  with  soda  ash  and  water,  rinsed,  and 
allowed  to  drain.  The  pumps  should  be  washed,  greased,  assem- 
bled, and  painted,  and  put  back  into  the  tank  again. 

The  soda  solution  from  the  tanks  should  be  pumped  over  the 
towers  for  2  hours,  when  the  interior  will  be  neutral.  If  the  shut- 
down is  to  be  long,  the  packing  and  lining  should  be  removed,  the 
inside  of  the  tower  washed,  dried,  and  painted,  and  then  the 
tower  sealed  tight. 

The  acid-soaked  coke  in  the  coke  filters  may  disintegrate  in 
time — it  does  not  always  do  so.  The  most  thorough  way  is  to 
remove  the  coke,  neutralize  it  with  lime  water,  wash  it,  wash  the 
filters,  paint  them,  and  replace  the  same  coke.  Then  seal  up 


216  AMERICAN  SULPHURIC  ACID  PRACTICE 

the  filters  tight.  Or  the  filters  may  be  simply  sealed  up,  taking 
a  chance  on  the  coke  standing  up. 

The  blower  must  be  washed  out  with  soda  water,  dried,  and 
painted.  All  bearings  must  be  greased.  The  cylinder  head  of 
the  engines  must  be  removed,  and  the  inside  of  the  cylinder 
greased. 

The  converter  mass  is  safer  inside  the  converter  than  anywhere 
else,  and  as  there  should  be  no  SO2  nor  SO3  nor  moisture  left 
inside  after  the  blowing  out  with  hot  air,  simply  blanking  off  the 
preheaters  and  converters  is  the  best  thing  to  do. 

The  absorber  house  can  be  treated  as  was  the  scrubber  house, 
with  the  addition  that  the  brick  linings  of  the  pump  tanks  should 
be  removed. 

All  acid  lines  should  be  washed  out  with  soda,  dried,  and 
blanked  off  in  sections,  all  valves  being  greased. 

All  iron  work,  such  as  on  the  buildings,  should  be  carefully 
painted. 


CHAPTER  XVIII 
PURIFICATION  OF  GASES 

In  the  Contact  Process,  to  get  any  reasonable  degree  of  con- 
version, the  gas  must  be  of  a  certain  concentration,  certain  tem- 
perature, and  CLEAN. 

Impurities  in  the  gas  are  both  mechanical  and  chemical,  and 
each  class  of  treatment  is  necessary. 

A  distinction  must  be  drawn  between  an  impurity  that  is 
merely  a  diluant,  and  one  that  has  in  itself  a  bad  effect  upon  the 
result,  either  from  its  effects  upon  the  system  or  upon  the  contact 
mass. 

The  first  class  is  well  represented  by  atmospheric  nitrogen, 
present  to  the  extent  of  77  per  cent  (by  weight)  in  the  air  drawn 
into  the  system.  This  means  that  about  four-fifths  of  the  gas 
handled,  cooled,  and  heated,  is  worthless;  but  this  handling  is 
more  economical  than  the  use  of  pure  oxygen  would  be.  The 
nitrogen,  also  the  minor  gases  of  the  atmosphere,  have  no  effect 
upon  the  contact  mass  nor  upon  the  life  of  the  system,  and  leave 
the  stacks  as  inert  as  they  were  upon  entering  the  burners. 

Mechanically-carried  dust  will  finally  stop  the  contact  action 
simply  by  covering  the  mass  and  preventing  its  coming  in  contact 
with  the  gas.  If  in  sufficient  quantity  it  might  clog  the  system. 

Moisture  dilutes  acid,  and  the  action  of  dilute  acid  is  well 
shown  in  Table  21,  Chapter  XXIII,  covering  the  action  of 
sulphuric  acid  of  various  concentrations  upon  iron. 

Sulphur  as  a  sublimate  will  crystalize  out  somewhere  in  the 
system,  possibly  causing  a  complete  block. 

Sulphur  trioxide  unites  with  water  vapor  to  cause  the  mist 
spoken  of  in  the  last  chapter. 

Arsenic,  antimony,  lead,  mercury,  selenium,  tellurium,  and 
silicon  tetra-fluoride  are  all  enemies  of  the  contact  process, 
chemically,  and  the  greatest  of  these  is  arsenic.  They  destroy 
almost  entirely  the  catalytic  action  of  the  platinum;  they  "poi- 
son" it;  and  the  action  cannot  be  reobtained  in  any  known  way, 
short  of  removing  the  mass,  recovering  the  platinum  in  the  form 
of  platinic  chloride,  and  making  up  the  mass  again. 

217 


218  AMERICAN  SULPHURIC  ACID  PRACTICE 

Arsenic  can  be  partly,  and  some  authorities  say  completely, 
removed  from  the  mass  by  passing  chlorine,  or,  better,  hydro- 
chloric acid  gas  through  the  mass,  and  then  removing  the  gas  by 
blowing  heated  air  through.  But  at  ordinary  converting  tem- 
peratures part  of  the  platinum  is  converted  into  chloride,  carried 
off,  and  deposited  somewhere  in  the  system. 

Lead,  mercury,  and  their  salts  form  compounds,  or  perhaps 
alloys,  with  platinum,  which  destroy  the  catalytic  properties 
of  the  platinum.  It  is  theoretically,  but  not  practically,  possible 
to  volatilize  the  lead. 

Nitric  acid  rapidly  destroys  iron  work. 

Silicon  tetra-fluoride,  chlorine,  and  hydrochloric  acid  stop  the 
catalytic  action  of  platinum  while  actually  present:  but  as  soon 
as  the  impurity  has  passed  by  the  action  goes  on  without  any  bad 
effect.  In  this  respect  these  impurities  differ  from  arsenic  and 
antimony. 

The  gas,  under  suction,  leaves  the  burners  not  far  from  500°C., 
carrying  with  it  all  or  any  of  the  impurities  mentioned  above. 

The  order  usually  observed  in  purifying  the  gas  is  to  remove 
first  the  sulphur  vapor,  then  dust,  excess  heat,  SOs,  arsenic  and 
the  other  contact  "  poisons/7  moisture,  and  the  sulphuric  acid 
"mist."  The  arsenic  may  be  partly  removed,  but  a  fuel  contain- 
ing much  of  it  will  soon  destroy  the  usefulness  of  the  mass,  so 
great  care  must  be  exercised  in  the  purchase  of  ores  or  sulphur. 

Although  SO2  begins  to  form  at  109°C.,  and  sulphur  melts  2° 
higher,  there  is  probably  always  some  unburned  sulphur  escaping 
from  the  burner,  due  to  incomplete  mixing  with  air.  The  tem- 
perature is  high  enough  to  burn  this  sulphur  vapor,  if  sufficient 
oxygen  is  present,  as  is  always  the  case  after  dilution  with  air 
at  the  back  end  of  the  burner.  This  results  in  combustion  in  the 
combustion  chamber,  and  in  cases  where  very  hot  burners  pro- 
duce large  quantities  of  unburned,  vaporized  sulphur,  even  back 
into  the  cooling  flue.  This  of  course  cuts  down  the  cooling  sur- 
face, and  throws  an  additional  load  upon  the  cooling  system, 
whatever  form  it  may  take,  which  follows. 

Dust  recovery  is  a  mechanical  problem,  the  dust  being  carried 
slowly  through  brick  dust  chambers,  sometimes  depending  solely 
upon  the  very  slowly  moving  gas  to  afford  an  opportunity  for 
the  dust  to  settle  out,  and  sometimes  equipped  with  baffle  plates. 
These  chambers  have  a  bottom  sloping  to  one  side,  and  at  the 
bottom  of  the  slope  iron  clean-out  doors.  One  of  the  many 


PURIFICATION  OF  GASES  219 

advantages  of  brimstone  over  pyrites  is  the  absence  of  dust;  no 
provision  at  all  need  be  made  for  it. 

As  the  bulk  of  the  dust  carried  over  comes  from  the  iron  oxides 
left  after  roasting  pyrites,  and  as  Fe2O3  is  an  active  catalytic 
agent,  particularly  at  the  temperature  of  the  dust  flue,  some  S03 
is  produced  at  this  part  of  the  line. 

This  dust  is  so  fine  that  without  some  method  of  agglutination 
it  is  practically  impossible  to  smelt  it.  It  is  free  enough  from 
sulphur  to  be  a  welcome  addition  to  a  blast  furnace  charge,  when 
properly  agglutinated — for  a  fair  sized  plant  a  sintering  machine 
of  the  type  described  in  Chapter  V  is  the  best  from  every  angle, 
but  briquetting  will  make  a  salable  product,  under  most  condi- 


FIG.  69. — Cooling  coils. 

tioris.  Large  lumps  usually  have  " green"  cores,  but  the  dust  is 
roasted  through  and  through.  I  speak  of  iron  furnaces  as  possible 
customers,  but  frequently  the  cinder  is  valuable  for  other  metals, 
as  copper  or  zinc,  and  if  the  pyrite  carries  gold  or  silver  there  is 
almost  certain  to  be  a  concentration  of  the  precious  metals  in 
the  dust  chamber,  due  to  their  votility. 

The  brick  walls  of  the  dust  chamber  are  very  poor  conductors 
of  heat,  so  there  is  little  cooling  effect  felt  in  the  chamber. 

The  first  fundamental  difference  between  the  Badische  and  the 
Schroder-Grillo  processes  is  in  the  method  of  cooling  the  gases. 

The  Badische  process  effects  the  cooling  by  evaporating  water. 
A  large  tower,  usually  8  ft.  in  diameter,  by  12  ft.  high,  receives 
the  gas:  and  within  that  tower,  where,  owing  to  the  ample  space, 


220  AMERICAN  SULPHURIC  ACID  PRACTICE 

the  gas  travels  slowly,  55°Be.  acid  trickles  down  over  broken 
quartz,  making  an  intimate  contact  with  the  gas.  At  this  con- 
centration of  acid,  the  gas,  at  its  temperature  of  500°C.,  simply 
distills  off  water,  great  clouds  of  steam  being  formed :  but  as  there 
is  no  decomposition  of  the  acid,  and  consequently  no  SOs  formed, 
there  is  no  mist.  Because  of  the  large  amount  of  water  removed 
as  steam,  it  is  constantly  necessary  to  "butt  down"  this  cooling 
acid. 

This  cooling  tower  must  not  have  any  exposed  iron  work,  as 
acid  of  such  low  concentration  attacks  it  very  rapidly.  The 
towers  are  usually  lead,  and  the  piping  and  tanks  lead-lined. 
The  pumps  are  hard  lead,  on  an  iron  frame.  Towers  are  some- 
times built  of  iron,  chemical  brick-lined,  but  any  leak  through  the 
lining  will  soon  let  through  enough  acid  to  attack  the  metal. 

Passage  through  this  cooling  tower  lowers  the  temperature  of 
the  gas  to  250°C.;  below  the  decomposition  point  of  the  real 
scrubber  acid.  The  gas  enters  the  second  tower,  which  is  much 
smaller  in  diameter  than  the  first,  or  cooling,  tower,  and  rises 
through  99  per  cent  H2SO4.  There  is  so  much  moisture  in  the 
gas  that  the  acid,  in  absorbing  this  moisture,  drops  1  per  cent 
in  its  passage  down  the  12  ft.  of  the  tower.  This  of  course 
necessitates  constant  "butting  up,"  .as  99  per  cent  is  at  the  top 
of  the  curve  of  vapor  pressures,  which  corresponds  almost  exactly 
with  the  absorbing  properties  of  sulphuric  acid.  The  gas  leaving 
the  tower  is  free  from  moisture. 

Experiments  with  the  use  of  88  per  cent  H2S04  for  cooling, 
showed  that  the  temperature  of  the  entering  gas  was  sufficient  to 
decompose  acid  of  that  concentration,  forming  a  large  amount 
of  mist.  Eighty-eight  per  cent  was  chosen,  as  it  is  the  lowest 
concentration  that  is  safe  to  apply  hot  to  iron  and  steel. 

The  Schroeder  process  removes  heat  by  radiation.  The  gas 
is  passed  through  a  long  iron  flue,  which  is  water  cooled,  usually 
by  passing  it  through  a  tank  of  water,  and  delivered  to  the  first 
scrubber  at  250°C.  This  temperature  is  low  enough  so  that  the 
scrubber  acid  is  not  decomposed.  When  running  on  pyrites 
lead  must  be  used  in  the  construction  of  this  flue,  because  enough 
H2SO4,  formed  from  the  moisture  in  the  air  and  the  SO3  formed 
by  the  catalytic  action  of  the  iron  oxides,  is  condensed,  to  destroy 
any  iron  work.  Only  if  the  temperature  of  the  gas  is  kept  up  to 
400°C.  is  it  safe  to  use  iron,  and  at  that  temperature  the  scrubber 
acid  is  decomposed. 


PURIFICATION  OF  GASES  221 

After  passing  the  scrubber  towers  what  little  acid  condenses  is 
cool  enough  and  strong  enough  not  to  be  harmful  to  cast  iron. 

In  the  writer's  experience  it  has  been  necessary  to  keep  the 
temperature  of  the  acid  in  the  first  scrubber  down  to  95°F.  to 
prevent  dissociation  of  acid,  and  consequent  formation  of  mist, 
twenty  cubic  feet  of  98  per  cent  acid,  at  95°F.,  will  cool  a 
thousand  feet  of  gas  at  450°  to  500°C.,  to  below  the  dissocia- 
tion temperature,  and  at  the  same  time  dry  it  thoroughly,  leaving 
it  entirely  free  from  moisture  or  mist. 

It  is  difficult  to  give  any  figures  on  the  amount  of  water  neces- 
sary to  cool  the  acid,  owing  to  local  conditions.  Water  in  the 
South,  particularly  if  from  shallow  rivers  or  ponds,  gets  warm 
enough  in  summer  to  seriously  complicate  the  cooling. 

It  may  be  assumed  that  no  fuel  having  over  a  trace  arsenic 
would  ever  be  used  for  the  contact  process,  so  that  no  company 
that  makes  lower  concentration  acid  by  diluting  fuming  with 
water  need  ever  fear  getting  any  arsenic  into  its  mass,  which 
should  last  indefinitely.  So  much  chamber  acid  carries  arsenic 
in  relatively  large  quantities  that  the  plant  that  depends  upon 
purchased  acid  for  the  weak  acid  it  requires  must  exercise  the 
greatest  and  most  constant  care.  If  the  gas  is  properly  cooled, 
so  that  no  mist  is  formed,  there  is  no  need  for  concern,  even  with 
a  considerable  amount  of  arsenic  in  the  scrubber  acid :  but  if  any 
mist  forms,  and  there  is  over  0.02  per  cent  arsenic  in  the  scrubber 
acid,  trouble  may  be  looked  for  with  confidence,  as  that  mist  is 
the  arsenic  carrier  par  excellence,  and  it  will  go  through  any  kind 
of  filter  or  scrubber  that  the  writer  has  ever  seen. 

Too  much  stress  cannot  be  laid  upon  proper  cooling,  for  only 
by  keeping  the  temperature  down  can  this  mist  be  prevented. 
Its  formation  must  be  prevented,  because  after  once  forming  we 
do  not  know  how  to  remove  it  from  the  gas. 

To  prevent  spashing  of  acid,  and  the  consequent  spray  that 
the  draught  will  carry  over,  two  devises  are  in  use.  The  acid 
may  be  introduced  onto  a  cast  iron  plate,  through  a  funnel. 
The  plate,  covering  the  entire  inside  diameter  of  the  tower,  is  as 
shown  in  Fig.  79.  Normally  the  acid  goes  through  the  many 
J^-in.  holes  onto  the  filler  inside  the  tower:  the  gas  rises  through 
the  2-in.  holes,  which  are  guarded  against  the  entry  of  acid  by 
the  surrounding  cast  iron  nipples,  and  thus  the  gas  gets  into  the 
space  above  the  plate  with  a  minimum  of  splashing.  When  the 
small  holes  become  clogged,  as  sometimes  happens,  the  acid  rises 


222  AMERICAN  SULPHURIC  ACID  PRACTICE 

high  enough  upon  the  plate  to  relieve  itself  through  the  large 
holes. 

The  other  method  is  to  pump  the  acid  to  a  reservoir,  from 
which  it  flows  gently  through  porcelain  tubes  to  the  surface  of 
the  filler. 

The  acid  must  be  delivered  at  the  top  of  the  tower,  as  it  flows 
down  by  gravity,  but  the  gas  may  pass  in  either  direction  that 
plant  convenience  dictates. 

The  cooling  coils,  filled  by  gravity  from  the  tower  are  cast 
iron  pipe,  usually  6  in.,  laid  horizontally.  The  acid  is  admitted 
into  the  lower  section  of  pipe,  so  that  water  dropping  first  upon 
the  top  pipe  and  then  on  to  the  lower  one  will  reach  the  coolest 
acid  first,  and  reserve  its  greatest  cooling  action,  by  evaporation, 
for  the  hot  acid  at  the  bottom. 

Figure  78,  in  Chapter  XIX,  showing  an  absorber  tower,  tank, 
and  equipment,  illustrates  equally  well  an  ideal  scrubber  tower. 

As  the  hot  gasses  direct  from  the  burner  have  greater  volume 
than  those  later  on,  it  is  customary  to  use  a  larger  tower,  or  two 
small  ones  in  parallel,  for  the  first  tower. 

The  amount  of  moisture  taken  out  of  the  air  drawn  through  it 
by  the  scrubber  system  is  large.  I  have  seen  a  plant  handling 
150,000  cu.  ft.  air  per  hour  remove  3,500  Ibs.  of  water,  in  24  hours, 
on  a  damp  day  in  winter  from  the  air,  and  over  6,000  Ibs.  in  summer. 

The  unit  of  a  scrubber  system  is  a  tower,  set  of  water  cooled 
cooling  pipes,  and  a  tank  with  a  turbine  pump.  For  our  ideal 
plant  a  tank  holding  100,000  Ibs.  of  acid  is  a  good  size.  This 
tank  should  be  horizontal,  6  ft.  X  24  ft.  of  %-in.  boiler  plate, 
unlined,  with  a  cleanout  hole  in  the  bottom,  turbine  pump  of  20 
cu.  ft.  a  minute  capacity,  set  through  a  manhole  in  the  top,  man- 
hole for  cleaning  out,  proper  connections  to  receive  and  discharge 
acid,  and  a  gauge  glass  in  the  end.  The  acid  is  pumped  to  the 
top  of  the  tower,  and  is  spread  by  a  distributer,  so  that  in  its 
passage  down  through  the  tower  it  comes  into  very  intimate 
contact  with  the  gas,  flows  from  the  towers  to  the  coolers  by 
gravity,  and  thence  back  to  the  tank. 

Do  not  depend  upon  the  gauge  glass  reading  for  accurate  in- 
formation about  the  quantity  of  acid  in  the  tank.  The  acid  that 
passes  up  into  the  gauge  glass  when  the  tank  is  filled  is  practically 
withdrawn  from  circulation,  and  retains  its  original  specific 
gravity.  So  as  that  in  the  tank  becomes  diluted  by  scrubbing, 
or  stronger  by  absorbing,  that  in  the  glass  will  float  upon,  or,  sink 


PURIFICATION  OF  GASES  223 

into,  this  acid  of  different  strength,  and  will  not  stand  at  the  level 
of  that  inside.  The  writer  has  found  5  in.  difference  between  a 
gauge  glass  and  a  stick  measurement. 

Each  tank  should  have  a  1-in.  vent  pipe,  leading  outside  the 
building,  to  relieve  the  pressure  caused  by  incoming  acid.  For 
sampling,  a  2%-in.  gate  valve,  or  a  2^-in.  nipple  and  cap  should 
be  set  in  the  top.  Do  not  use  a  tapped  hole  and  plug,  as  plugs 
stick  badly,  rough  handling  with  a  wrench  makes  them  loose 
their  corners  quickly,  and  then  they  are  very  hard  to  get  out.  A 
cap  on  a  nipple  is  much  better,  and  a  gate  valve  best  of  all. 

Types  of  pumps  are  discussed  in  Chapter  XIX. 

The  towers  of  different  designers  vary  greatly,  although  all  have 
the  same  function:  to  bring  into  intimate  contact  the  scrubber 
acid  and  the  gas.  Twelve  feet  high  seems  to  be  the  only  com- 
mon dimension.  The  internal  diameter  varies  from  3  ft.  6  in. 
to  8  ft.,  they  may  be  lined  with  lead  or  acid-resisting  brick,  set 
in  Pecora  or  other  acid-resisting  cement,  and  filled  with  broken 
quartz,  chemical-ware  rings,  or  cast-iron  filling  pieces. 

The  cooler  pipes,  always  warm,  afford  excellent  opportunities 
for  the  growth  of  any  water  plants,  particularly  those  of  a  slimy 
nature,  and  slime  and  mud  collect  upon  them  very  quickly. 
Any  foreign  matter  acts  as  an  insulator,  and  should  be  removed 
at  once.  Rubbing  with  a  piece  of  burlap  is  the  best  way  to 
clean  these  pipes,  although  a  broom  will  do  a  fine  job. 

The  current  of  gas  carries  some  acid  along  with  it  mechani- 
cally, and  some  method  of  mechanical  condensation  and  filtera- 
tion  is  necessary  to  remove  it.  A  large  tower  filled  with  pea 
coke,  followed  by  another  filled  with  buckwheat  size,  each 
tower  having  a  trapped  drain  in  the  bottom,  will  remove  most 
of  the  spray,  and  a  good  part  of  the  mist  that  forms.  These 
towers  should  be  large  enough  (not  under  10  ft.  in  diameter)  to 
permit  a  slow  movement  of  the  gas,  and  should  have  a  depth 
of  at  least  10  ft.  of  coke,  with  ample  space  at  the  top  and  bottom, 
for  entrance  and  exit  of  gas.  In  practice  about  as  many  plants 
take  the  gas  in  at  the  top  and  release  it  at  the  bottom  as  do  it  the 
other  way.  The  writer  prefers  to  remove  the  gas  from  the  top, 
believing  that  in  the  open  space  at  the  bottom,  with  acid  dripping 
from  the  coke  above,  some  new  spray  is  formed,  which  is  carried 
along  by  the  suction.  When  a  tower  is  newly  packed  there  is 
undoubtedly  some  dust  taken  along  from  the  top,  but  the  coke 
soon  becomes  damp  enough  to  prevent  this. 


224  AMERICAN  SULPHURIC  ACID  PRACTICE 

The  quantity  of  spray  caught  will  vary,  but  will  be  sufficient 
to  make  the  installation  of  a  small  blow  case  to  save  the  drip  well 
worth  while.  It  should  be  so  piped  that  all  the  coke  towers,  or 
"spray  catchers,"  run  into  it,  and  can  run  to  a  storage  tank. 

While  much  mist  is  condensed  by  the  coke,  enough  is  still 
left  in  the  gas  to  make  further  filtration  necessary.  While 
cotton  is  occasionally  recommended  as  a  filtering  medium,  I 
have  never  known  it  to  last  a  week.  The  condensed  acid  is 
strong  enough  to  carbonize  the  cotton  rapidly,  even  in  the  cold, 
causing  it  to  turn  to  a  black  dust — of  course  worthless 
for  filtering. 

So  asbestos  fibre  has  come  to  be  the  one  material  used.  It 
is  picked  over,  usually  by  hand,  to  break  up  the  lumps  it  packs 
into  during  handling  and  storage,  and  is  then  blown  by  a  light 
current  of  air,  which  "fluffs"  it.  The  apparatus  required  is  a 
covered  wooden  trough,  with  air,  controlled,  by  a  hand  valve, 
admitted  at  one  end  through  a  J^-in.  pipe.  The  fibre  is  blown 
down  the  trough  to  a  large  box,  with  one  side  made  of  burlap, 
through  which  the  air  escapes.  The  longest  staple  asbestos 
possible  should  be  procured.  Grade  201 A  of  the  H.  W.  Johns 
Manville  Co.  is  an  excellent  product.  On  account  of  the  light- 
ness of  the  asbestos  fibre  it  is  necessary  to  bring  the  gas  in  at  the 
top,  driving  it  down  through  the  filter:  otherwise  the  strength 
of  the  draught  will  carry  it  away.  A  good  form  of  filter  is  a 
set  of  cylindrical  tanks,  three  or  four  in  number,  6  ft.  in  diameter 
by  4  ft.  high,  in  parallel,  with  a  screen  of  %-in.  boiler  plate, 
punched  with  J^-in.  holes,  set  on  lugs  12  in.  from  the  bottom. 
There  are  usually  two  sets  of  these  filters,  in  series. 

The  fibre  is  spread  smoothly  over  this  screen,  to  a  depth  of 
15  in.;  7.5  sq.  ft.  filtering  surface,  per  hundred  pounds  of  sulphur 
burned  per  hour,  in  each  series  will  do  good  work,  and  will  require 
a  little  over  a  pound  of  fibre  per  square  foot  every  time  they 
are  packed. 

These  filters  work  better  when  moist,  so  moisture  in  itself  is 
harmless.  But  where  there  is  arsenic  in  the  mist  the  filters  will 
rapidly  become  impregnated  with  it  and  must  be  cleaned  to 
prevent  the  arsenic  from  reaching  the  converter  mass.  When 
the  filters  are  drained  constantly  there  is  less  necessity  for 
frequent  cleaning  than  where  the  condensate  is  allowed  to 
accumulate  in  the  bottom,  to  be  removed  at  intervals. 

Cleaning  simply  consists  in  removing  the  manhole  cover  and 


PURIFICATION  OF  GASES 


225 


taking  out  the  old  asbestos  with  a  fork,  then  spreading  the  new. 
The  blower  must  be  stopped  while  the  work  is  under  way. 
Only  experience  can  tell  how  often  it  is  necessary  to  repack 
filters — one  plant  may  need  it  every  3  weeks,  another  every 
6  months.  When  the  asbestos  is  soggy  it  is  time  to  repack  it, 
but  being  damp  will  do  no  harm  at  all. 

All  attempts  to  regenerate  the  asbestos  have  failed,  not  that 
it  is  hard  to  wash  out  the  acid,  but  that  wet  asbestos  packs  into  a 
cement. 

Unslacked  lime,  nut  or  pea  size,  has  been  tried  as  a  filtering 
material,  and  does  its  work  well,  but  is  hard  to  keep  open,  as  the 
calcium  sulphate  formed  crumbles,  and  the  dust  packs.  Also, 
the  condensed  acid  is  lost. 


FIG.  70. 


The  Tetelow  Chemical  Co.  uses,  on  gases  that  contain  a  little 
chlorine,  a  weak  milk  of  lime  wash,  where  first  a  bisulphite  is 
formed  with  the  SO2,  which  reacts  with  and  retains  the  chlorine. 

The  Tyndall  test  shows  any  mist  in  the  gas  that  is  invisible  to 
the  naked  eye.  An  apparatus,  shown  in  Fig.  70,  consists  of  C, 
a  small  flask  with  a  rubber  stopper,  through  which  two  glass 
tubes  pass,  and  A,  a  lens,  the  focus  of  which  is  just  beyond  the 
flask:  all  enclosed  in  a  wooden  box,  painted  black  inside.  The 
flask  is  filled  with  the  gas  to  be  tested,  either  by  direct  pressure, 
or,  if  on  the  suction  end  of  the  system,  by  an  aspirator  bottle, 
the  ends  of  the  tubes  corked,  the  flask  replaced  in  the  box,  and 
a  beam  of  sunlight  directed  through  the  gas  in  the  flask,  via 
the  lens.  If  there  is  any  mist  it  will  show  in  the  path  of  the 
beam  as  the  motes  dance  in  a  beam  of  sunlight  in  the  old  dusty 

15 


226  AMERICAN  SULPHURIC  ACID  PRACTICE 

attic.     But  if  the  gas  is  dry  a  disk  of  light  shows  on  the  side  of 
the  flask  where  it  passes  through  the  glass,  and  that  is  all. 

If,  through  faulty  design,  it  is  impossible  to  prevent  the 
formation  of  this  mist,  this  arsenic  carrier,  the  greatest  efforts 
must  be  made  to  remove  as  much  of  it  as  possible,  because 
arsenic  is  more  liable  to  get  into  the  system  via  the  scrubber 
acid  than  through  the  fuel  burned,  and  if  there  is  no  mist  this 
arsenic  will  not  be  taken  from  the  acid,  ultimately  getting  to 
the  converter  mass. 


< 


_H 
Jj 


FIG.  71. — Roots  blower. 

Without  proper  provision  for  cooling  mist  will  form.  One 
of  the  plants  built  in  a  hurry  to  respond  to  the  demand  for 
fuming  acid  at  the  beginning  of  the  European  War,  in  1915, 
was  not  provided  with  sufficient  cooling  area,  and  although 
operated  with  great  skill,  and  giving  in  all  respects  but  this  very 
satisfactory  results,  showed  all  the  bad  effects  of  insufficient 
cooling — the  filters  had  to  be  cleaned  very  frequently,  arsenic 
went  through  to  the  converter  mass,  and  the  exit  stacks  were 
always  fogging. 

The  blower  is  placed  at  the  end  of  the  scrubber  system,  so 
that  the  maximum  pressure  may  be  available  to  force  the  gas 


PURIFICATION  OF  GASES  227 

through  the  converter  mass.  This  blower  is  always  a  valveless, 
direct-acting  blower,  of  the  Roots  type.  These  engines  are  so 
well  known  that  any  extended  description  is  unnecessary. 
They  may  be  built  either  direct  connected  to  a  steam  engine, 
or  to  be  belted  to  shafting  or  a  motor,  and  act  over  a  very  wide 
range  of  speeds  very  efficiently.  The  usual  guarantee  is  that  the 
slip  will  not  exceed  15  per  cent.  As  the  rotors  have  H28~m- 
clearance,  and  no  sliding  surfaces,  these  engines  have  a  very 
long  life.  The  small  clearance  is  not  sufficient  to  cause  much 
slip.  If  a  sudden  stop  in  the  suction  line  occurs  the  partial 
vacuum  formed  will  cause  the  blower  to  reverse  itself  for  several 
revolutions,  against  the  steam  pressure. 

If  arranged  this  way,  the  pressure  at  the  engine  is  almost  twice 
the  suction,  mainly  because  of  the  resistence  offered  by  the 
converter  mass:  but  also  because  there  are  usually  more  showers 
in  the  absorber  house  than  in  the  scrubber  house.  Our  ideal 
unit  will  show,  for  normal  running,  about  12  in.  of  water  suction 
at  the  blowers. 


CHAPTER  XIX 
CONVERTING 

The  second  step  in  making  Sulphuric  Acid  by  the  Contact 
Process  is  the  conversion  of  862  to  SO3,  by  bringing  it  into 
intimate  contact,  at  a  suitable  temperature  with  finely  divided 
platinum. 

A  mixture  of  SO2  with  air  will  slowly  oxidize  to  SO3,  but  so 
slowly  that  this  action  is  valueless  from  a  commercial  stand- 
point. Many  substances  have  a  catalytic  action  upon  this 
chemical  reaction,  that  of  Fe2O3  and  Fe3O4,  among  the  common 
substances,  being  very  marked.  All  the  metals  of  the  platinum 
group  posses  this  activity,  but  none  other  to  the  extent  that 
platinum  itself,  in  a  finely  divided  state,  does. 

The  catalyzer  itself  is  entirely  unacted  upon,  and  its  simple 
presence  is  all  that  is  necessary.  The  effect  is  without  doubt 
adsorbtion,  or  condensation  of  gas  upon  the  surface  of  the 
catalyzer.  When  glass  is  wet  by  water  the  water  is  not  absorbed 
— it  is  held  however  by  the  force  we  call  adsorbtion — and  some 
solids  have  this  effect  upon  some  gases.  It  is  probable  that 
there  is  a  Concentration  of  gas  in  a  condition  to  react,  and  by 
the  law  of  Mass  Action  the  reaction  must  be  hastened.  Reason- 
ing along  these  lines,  the  plan  of  the  Davison  Chemical  Co.  to 
use  liquid  SC>2,  recovered  from  fume  stacks  by  their  new  silica 
gel  process,  should  give  high  yields  and  capacity,  because  of  the 
"strong"  gas  used. 

Six  factors  enter  into  the  conversion:  catalytic  agent,  which 
is  always  finely  divided  platinum;  sulphur  dioxide;  air,  supplying 
oxygen;  temperature;  time,  and  impurities. 

The  Badische  process,  worked  out  mainly  by  Rudolf  Knietsch, 
uses  platinized  asbestos  as  a  catalizer,  a  solution  of  platinic 
chloride  being  sprayed  over  the  asbestos  fibre,  which  is  then  put 
into  the  converters  and  dried.  The  mass  then  looks  like  wool 
died  a  lemon  yellow,  is  soft  and  fluffy,  and  is  not  subjected  to 
any  furnacing  at  all.  It  dries  out  very  rapidly  in  the  converter, 
the  chlorine  of  the  platinic  chloride  is  driven  off,  and  metallic 
platinum  left  in  an  extreme  state  of  division. 

The  Badische  conversion  unit  is  made  up  of  a  preheater,  used 

228 


CONVERTING 


229 


for  starting  up  and  in  emergencies,  two  converters  and  three 
transfers.  The  drawing  shows  the  general  arrangement  of  the 
converter — the  gas  enters  at  I,  filling  the  space  A,  goes  up  the 
closed  bottom  tubes  B,  and  down  through  C  containing  the 
converter  mass,  into  D,  and  through  the  outlet  0  to  the  absorb- 
tion  system.  C  is  made  about  three  inches  in  diameter,  to 
provide  for  uniform  cooling  of  the  mass  by  the  incoming  stream 
of  cold  S02  and  air.  It  is  this  form  of  converter  that  gives 
the  Knietsch  process  its  economy  of  fuel,  and  is  patented  in  this 
country  under  United  States  patents  652,119,  688,020,  and 


FIG.  72. 

823,472,  dated  respectively,  June  19,  1900,  December  3,  1901, 
and  June  12,  1906.  Of  these  652,119  is  the  fundamental  one, 
the  others  being  modifications  thereof.  See  fig.  70. 

The  Schroeder-Grillo  process  uses  platinum  deposited  upon 
magnesium  sulphate  for  the  mass. 

Pure  magnesium  sulphate,  with  the  water  of  crystalization 
driven  off,  is  coated,  not  impregnated,  with  platinum  to  the 
extent  of  0.3  per  cent  of  its  weight.  This  gives  a  very  large 
surface,  as  the  salt  in  this  state  is  very  porous,  and  the  platinum 
is  spread  out  thin  over  a  wide  area.  The  magnesium  sulphate 
is  spread  out  upon  a  flat  surface,  6  in.  thick,  and  the  platinic 
chloride  is  sprayed  on  through  glass  nozzles  connected  by  rubber 
tubing  to  the  bottles  of  solution,  the  bottles  being  supplied  with 
air  under  pressure.  At  intervals  the  mass  is  turned  over  with 


230  AMERICAN  SULPHURIC  ACID  PRACTICE 

wooden  shovels,  as  it  is  of  the  utmost  importance  to  get  the 
platinum  on  evenly. 

The  sprayed  mass  is  then  put  into  the  furnace  previously 
used  to  dry  the  magnesium  sulphate,  and  heated  to  redness  for 
half  an  hour.  By  this  time  all  the  chlorine  has  been  driven 
off,  leaving  the  platinum  in  an  extreme  state  of  division. 

The  mass  is  then  allowed  to  cool  and  is  put  into  tight  cans, 
weighed,  and  put  away  until  needed,  as  it  will  keep  indefinitely. 

Usual  practice  is  4.5  per  cent  of  platinum  on  the  weight  of  SO2 
per  hour.  This  will  give  a  97  per  cent  conversion  with  good 
handling.  A  smaller  proportion  of  platinum  will  give  a  lower 
conversion,  and  in  each  case  it  must  be  determined  whether  it  is 
better  to  have  a  smaller  investment,  and  loose  more  S02  out  of 
the  stacks.  For  instance,  %  the  platinum  investment  will  about 
double  the  stack  loss — 2J£  per  cent  platinum  on  the  hourly  SO2 
will  give  about  95^£  per  cent  conversion,  other  conditions  being 
equal  to  the  97  per  cent  conversion  with  5  per  cent  platinum. 

The  sulphur  dioxide  and  air  are  intimately  mixed  in  their 
passage  through  the  burners,  scrubbers,  and  blowing  engines, 
and  are  freed  from  impurities  as  much  as  possible,  so  that  the 
gas  entering  the  converters  contains  SO2  and  0  as  active  agents, 
and  the  nitrogen  and  other  inert  gases  of  the  air  as  diluants. 

Dr.  C.  L.  Reese  has  proved  experimentally  that  moisture 
present  will  not  affect  the  mass,  but  as  of  course  acid  would  be 
formed  the  plant  would  suffer.  C02  is  harmless.  The  worst 
of  the  impurities  liable  to  be  encountered  is  arsenic,  which 
" poisons"  the  mass  by  forming  a  glassy  coating  of  a  salt  of 
arsenic  and  platinum,  as  little  as  2  per  cent  of  As  on  the  weight 
of  platinum  being  sufficient  to  render  the  mass  inert.  Dr. 
C.  L.  Reese  says  that  As  can  be  removed  from  the  mass  by 
passing  HC1  in  with  the  gas  mixture,  but  my  advise  is  not  to 
let  any  get  into  the  mass — the  action  seems  to  be  that  the  As 
coating  simply  encloses  the  platinum  so  that  it  cannot  come 
into  contact  with  the  gas  mixture. 

Dust  of  all  kinds  has  a  purely  mechanical  covering  action, 
which  is  just  as  effective  as  the  arsenic  in  preventing  contact, 

H2S04  "gums  up"  the  mass,  making  it  difficult  to  penetrate. 

TEMPERATURE 

2SO2  +  O2  =  2(SO3  +  40250  B.T.U.),  on  the  authority  of 
Prof.  J.  W.  Richards.  The  reaction  proceeds  slowly  at  low 


CONVERTING 


231 


temperatures,  really  beginning  at  about  200°C.,  and  continuing 
to  increase  in  velocity  with  rising  temperature.  However, 
the  reaction  is  reversible  and  above  420°C.,  decomposition  of 
SOs  sets  in,  becoming  more  marked  with  further  increase  of 
temperature,  until  at  1,000°C.  SO3  cannot  exist,  in  the  presence 
of  the  catalizer. 

The  best  temperature  to  carry  is  entirely  dependent  upon  the 
condition  of  the  mass  and  the  "strength"  of  the  entering  gas, 


,-  Faced ancf  Prilled. 


•     ,  „ 

- S'-8  • \ 

LIST  Connection 

/  Bottom  Section 
5  Intermediate  Sections 
I  Cover 
I  Connection 
I  Center  Support- 2 -4  " 
4-  Center  Supports  -19 ' 
30  Orate  Sections 
16  -li  "xS'-T1  Round  Steel  Reds 

T.d.  f.  3  "with  Huts  and  Washers 


^       ^.  ^Flanges  on  A>,    v,. 
"^N    £ij  ^  Sections,  Flang<?a\     "~^- 


A- 


>S         L-LLJ- 

I    h#^ 


Section  A -A 
Center  Support 


FIG.  73. 

and  it  will  vary  with  variations  in  these  two,  and  therefore  is 
a  purely  local  condition.  From  375°C.  to  425°C.  is  about  right. 

The  entering  gases  must  be  heated  sufficiently  to  start  the 
reaction,  as  they  have  been  well  cooled  by  the  scrubbing,  and 
the  converted  SO3  must  be  cooled  before  absorbtion. 

Here  lies  the  fundamental  difference  between  the  Badische 
and  the  Schroeder-Grillo  processes — the  former  makes  its 
converter  into  a  heat  exchanger,  and  heats  its  entering  gases  by 
taking  the  excess  heat  from  its  SO3,  where  the  latter  uses  fuel 
to  heat  up,  and  then  wastes  the  heat  generated  in  the  converter. 

The    Badische    conversion    unit    has    been    described.     The 


232 


AMERICAN  SULPHURIC  ACID  PRACTICE 


Schroeder-Grillo  unit  is  a  vertical  cylinder  of  cast  iron,  5  to  8  ft. 
in  diameter,  built  up  in  18  in.  to  2  ft.  sections,  flanged,  joints 
packed  with  asbestos  wicking,  all  held  together  by  stay  bolts 
from  the  top  to  the  bottom  flanges.  Each  section  contains  a 
perforated  cast  iron  floor,  upon  which  lies  J^-in.  mesh  iron  wire 
screen,  and  upon  this  the  mass.  There  are  usually  5  sections 
to  a  converter,  and  4  converters  to  a  unit.  For  a  converter 
7  ft.  outside  diameter  the  normal  amount  of  mass  is  7500  .Ibs. 
evenly  divided  among  the  5  trays,  and  carrying  0.3  per  cent  Pt. 
That  means  about  $190,000  worth  of  platinum  at  today's  (No- 
vember, 1919)  prices,  of  $145  per  ounce.  Such  a  plant  will  burn 
1000  Ibs.  of  sulphur  an  hour. 


FIG.  74. 


During  the  war,  at  one  large  plant,  the  quantity  of  mass  was 
cut  in  half,  concentration  (per  cent  of  Pt)  remaining  .the  same. 
This  dropped  the  conversion  from  97  per  cent  to  between  94 
per  cent  and  95  per  cent — this  brings  up  the  question  of  the  bal- 
ance between  stack  losses,  which  represent  raw  material,  power, 
and  labor,  and  the  investment  in  platinum.  This  will  be  con- 
sidered in  the  chapter  on  accounting. 

Good  recording  pyrometers  are  absolutely  necessary  for  con- 
ducting this  operation.  Leeds  &  Northrup,  Philadelphia; 
Industrial  Instrument  Co.,  Foxboro,  Mass.;  and  the  Taylor 
Instrument  Co.,  Rochester,  N.  Y.,  can  be  depended  upon  to 
furnish  good  ones. 

The  Schroeder-Grillo  preheater  is  a  brick  box,  full  of  6-in. 


CONVERTING 


233 


boiler  tube  pipe,  vertically  set,  flanged,  connected  by  return 
bends,  through  which  the  gas  passes  to  the  converters,  all  heated 
by  coal  or  oil  fires,  flue  gases  passing  around  the  outside  of  the 
pipes.  For  a  plant  burning  1,000  Ib.  sulphur  per  hour,  4  con- 
verters, each  5  sections  high,  will  be  used,  and  the  preheater  to 
each  one  will  contain  250  ft.  of  6-in.  pipe,  plus  the  return  bends. 
The  pipe  is  set  vertically  to  prevent  flue  dust  from  settling  on  it, 
insulating  the  gas  inside.  Such  a  plant  will  use  6  tons  of  steam 


FIG.  75. 

coal  daily  in  summer,  7  to  8  in  winter.  On  1919  coal  prices,  that 
is,  over  50  cts.  per  1,000  Ib.,  100  per  cent  acid  produced — well 
worth  saving.  But  even  with  this  high  fuel  cost,  the  writer 
prefers  this  system  to  that  of  the  Badische  because  of  its 
simpler  operation. 

The  gases  from  the  Schroeder-Grillo  converters,  consisting  of 
N,  SO3,  unconverted  SO2,  and  impurities  (mighty  few  of  these 
however)  are  at  a  temperature  around  350°C.,  much  too  hot  for 


234 


AMERICAN  SULPHURIC  ACID  PRACTICE 


absorption;  so  they  are  cooled  by  passing  through  250  ft.  of  cast 
iron  pipe,  set  horizontally,  between  headers,  and  arranged  to 
have  a  spray  of  water  drip  over  them  in  warm  weather.  These 
pipes  must  be  equipped  with  drain  cocks,  because  upon  starting 
up  there  is  always  some  moisture  in  the  mass,  which  will  come 
from  the  hot  converters  as  sulphuric  acid  vapor,  and  will  condense 
here,  effectually  trapping  the  system  if  not  removed. 

Time  of  contact  is  controlled  by  the  blowing  engine,  and  will 
vary  so  with  the  plant  that  no  rule  can  be  laid  down.     For  the 


FIG.  76. 

size  of  blowing  engine  figure  the  volume  of  gas  necessary  to 
provide  a  7  per  cent  gas  for  the  sulphur  to  be  burned,  at  80°F. 

The  only  pressure  is  that  of  the  blowing  engines,  sufficient  to 
overcome  the  friction  of  the  system,  and  keep  the  current  of  gas 
moving. 

The  early  experimenters  thought  a  stoicometric  mixture  of 
SO2  and  O  necessary  to  get  a  good  conversion,  but  were  never 
able  to  convert  over  77  per  cent  of  their  SO2,  and  then  only  under 
laboratory  conditions.  The  production  of  pure  oxygen  was 
expensive,  and  later  proved  a  needless  expense,  as  air  was  shown 
to  give  excellent  results,  the  nitrogen  having  no  deleterious  effect 
whatever. 


CONVERTING  235 

Ferric  oxide  comes  to  its  maximum  as  a  catalytic  agent  at 
675°C.,  at  a  point  where  the  dissociation  of  S03  is  very  marked, 
which  eliminates  it  as  a  possible  contestant  with  platinum. 

It  is  necessary  to  use  a  catalytic  agent  that  will  do  maximum 
work  at  or  under  450°C.,  and  platinum  is  the  only  one  known  so 
far. 

Some  experimental  work  along  the  lines  of  colloidal  precipita- 
tion of  the  platinum  upon  the  mass  have  been  done,  notably  by 
Botho  Schwerin,  in  U.  S.  patent  1,098,  176,  owned  by  the  Chemical 
Foundation,  81  Fulton  St.,  New  York.  In  view  of  the  fact  that 
the  investment  is  the  greatest  part  of  the  cost  of  contact  acid, 
anything  to  increase  the  surface  of  platinum  exposed  will  pay 
well,  and  should  be  followed  up. 

Kurt  Albert,  in  U.  S.  patent  1,018,402,  also  owned  by  the  Chemi- 
cal foundation,  claims  to  have  reached  a  94  per  cent  yield  with 
iron  and  strontium  oxides  as  a  catalyzer.  This  with  the  Davison 
adsorption  system  on  the  exit  stacks  to  prevent  the  loss  of  uncon- 
verted S02  offers  a  fertile  field  for  research. 

Dr.  Knietsch  formulated  the  law  of  mass  action  as  follows  : 


S02  ~  1 

when  K  =  concentration  in  volume  per  cent.  This  shows  the 
conversion  we  may  obtain,  but  nothing  about  velocity  of  reaction 
or  proper  temperature. 

Each  plant  must  develop  its  own  suitable  working  conditions, 
and  adhere  as  closely  as  possible  to  them.  If  the  operator  starts 
out  to  make  a  7  per  cent  "gas"  —  7  per  cent  by  volume  —  he  will 
not  be  far  wrong. 

Although  it  is  necessary  to  dry  the  gas  as  much  as  possible,  an 
absolutely  dry  gas  will  stop  the  reaction.  It  is  not  possible  to 
remove  the  last  traces  of  moisture  with  our  scrubbing  systems,  but 
they  remove  all  that  might  be  dangerous,  as  an  excess  would  be. 

Uniformity  of  temperature  is  of  the  utmost  importance  —  the 
control  should  be  within  5°C.  If  the  mass  is  injured  in  any  way 
it  is  likely  to  require  a  higher  temperature  to  get  conversion,  and 
that  is  about  the  only  way  there  is  of  detecting  mass  "  poisoning.  " 

GAS  CONTROL 

The  Reich  test  for  SO2  in  gas,  with  the  pyrometer  readings,  is 
our  guide.  This  test  is  conducted  as  described  in  Chapter  XIV. 


236  AMERICAN  SULPHURIC  ACID  PRACTICE 

The  laboratory  should  occasionally  check  this  by  the  K2CO3. 
test. 

This  gas  test  should  be  made  not  less  often  than  every  2  hours, 
on  both  the  entrance  and  exit  gases.  Be  sure  the  gas  passes 
through  the  apparatus  for  a  minute  before  each  test,  to  make 
certain  that  it  is  the  gas  of  the  present,  not  of  2  hours  ago,  that 
is  being  tested.  Quarter  inch  pipes,  led  off  of  the  gas  mains, 
and  controlled  by  valves,  bring  the  gas  to  the  test. 

In  figuring  conversion  after  the  test,  it  must  be  borne  in  mind 
that  the  volume  of  gas  is  decreased  by  the  amount  of  oxygen  the 
SC>2  has  taken  in  its  oxidation. 

SLIDE  RULE  FOR  S02  TO  SO3  CONVERSION  1 
In  general,  if  an  equation  can  be  written  in  the  form 

f(x)  -  f(y),  f(2) 

a  slide  rule  may  be  so  constructed  that  the  value  of  any  variable 
can  be  found  if  the  others  are  known.     As  a  simple  illustration, 
consider  the  computation  of  conversion  in  the  contact  process  for 
the  manufacture  of  sulphuric  acid. 
Let  a  =  per  cent  by  volume  of  SOz  in  entrance  gas, 
b  =  per  cent  by  volume  of  S02  in  exit  gas, 
c  =  per  cent  conversion  =  per  cent  S02  converted 

to  SO3. 

These  quantities  are  related  by  the  equation 
_  10,000  (a  -  b) 


This  form  of  equation  is  not  suitable  for  the  construction  of 
a  slide  rule,  but  it  may  be  rewritten  as 

JL_       /10°  _  5\  ...  /10Q  _  ?\ 
100       \  a        2/    '    \  b        2/ 


%  SC>2  in  Entrance  Gas 


~-|  °-5l,'  "i.'ol   '  '  b.'ol 

%  SO 2  in  Exit  Gas  V 

'    '    '    I  '   '    '    I    U,r i        ' ' 


|80'        '    |90     "    [95 
Conversion 


FIG.  76A. 

SO2  —  SO3  slide  rule  set,  10  per  cent  entrance,  0.7  per  cent  exit 
=  94  per  cent  conversion. 

1  From  Chemical  and  Metallurgical  Engineering,  September  15,  1919. 


CONVERTING  237 

The  slide  rule  scales  for  the  solution  of  this  equation  are  in  the 
accompanying  figure.     The  upper  scale  is  laid  off  proportionally 

/100      3\    .,       ...         .       /100      3\ 
to  log  ^ — •  —  2] »  the  slide  to  log  I-g g/  > anc* tne  l°wer  scale 

to  log  ( 1  —  TQQ)  "     These  scales  are  laid  off  from  right  to  left  so 

that  the  marked  values  a,  b,  c  will  increase  from  left  to  right, 
as  this  is  the  most  natural  method  of  reading  scales.  The  proper 
values  of  SO 2  in  burner  gas  and  exit  gas  are  set  together,  and  the 
conversion  read  opposite  the  arrow.  The  zero  point  (i.e.,  logl) 
of  the  lower  scale  is  moved  to  the  left  relative  to  the  upper  one, 
to  make  the  rule  more  compact,  and  the  arrow  displaced  the  same 
distance  to  give  the  correct  reading. 


CHAPTER  XX 
ABSORBTION 

As  stated  briefly  in  Chapter  XII,  water  is  not  a  satisfactory 
absorbing  agent  for  80s,  and  as  the  water  in  diluted  H2S04  acts 
like  water,  it  is  necessary  to  use  strong  (not  less  than  98.3  per 
cent)  sulphuric  acid.  You  might  say  that  the  gas  is  scrubbed 
with  the  absorbing  medium,  for  the  apparatus  used  is  a  gas 
scrubber  of  some  type,  the  object  being  to  get  as  intimate  an 
association  as  possible  of  the  gas  and  the  acid. 

If  sulphuric  acid  of  less  than  98.3  per  cent  is  heated  in  an  open 
pan  at  350°C.  water  will  distill  off  until  this  ''critical"  point, 
i.e.,  98.3  per  cent  is  reached — if  the  original  acid  is  of  a  higher 
concentration  than  the  " critical"  strength,  SO3  will  come  off 
until  the  strength  drops  to  98.3  per  cent — after  it  has  reached 
that  point  however  it  comes  over  at  that  strength  until  the  end. 
Of  course  pan  concentration  cannot  go  to  this  point  profitably, 
because  the  losses  by  entrainment  increase  very  fast  with  the 
strength  of  the  pan  acid. 

At  98.3  per  cent  and  100°C.  sulphuric  acid  has  a  minimum 
vapor  pressure  in  vacuo,  and  at  this  point  its  sp.g.  is  the  highest. 
At  this  point  absorbtion  of  SOs  is  practically  100  per  cent. 

The  heat  of  combination  of  S03  and  H20  is  180,540  B.T.U., 
according  to  Richard's  "  Metallurgical  Calculations,"  which 
runs  the  temperature  in  the  absorbing  apparatus  up  to  the  point 
where  cooling  is  always  necessary.  This  is  usually  done  by 
circulating  the  absorbing  acid,  keeping  a  large  volume  in  service, 
and  cooling  the  storage  tank  and  circulating  system  with  water. 
The  first  tower  will  require,  for  a  unit  plant  of  1000  Ibs.  S  per 
hour,  not  less  than  250  ft.  of  cooling  pipe,  aside  from  necessary 
connections. 

As  fuming  acid  is  very  hard  on  iron  or  steel,  tanks  and  towers 
must  be  carefully  lined  with  an  acid-resisting  material.  The 
writer  does  not  think  much  of  any  of  the  asphalt  bitumens  that 
are  used  for  this  purpose,  prefering  a  good  acid-proof  tile,  well 
laid  in  acid-proof  cement.  The  cost  of  towers  thus  protected 
is  high,  but  worth  that  cost. 

238 


ABSORBTION 


239 


As  the  strength  of  the  acid  in  the  tower  increases,  so  does  the 
vapor  tension,  and  the  absorbing  qualities  fall :  also  the  tempera- 
ture being  high  works  against  good  absorbtion,  so  it  is  usual 
to  arrange  6  towers  in  series,  fresh  acid  being  added  in  the  last 
one,  at  intervals,  the  towers  nearer  the  first  one  being  replenished 
from  those  behind,  and  the  acid  made  being  drawn  from  No.  1. 
The  temperature  in  the  later  towers  is  progressively  lower  than 


60 


1Q      &0      90 
%  H2  SO4 
Partial  pressure 
due  to  water 


100 
I 


20      30      40       50      60       70 

%  Free  SOa 
Partial  pressure  due  to  SO  3 

FIQ.  77. 


80      90     100 


in  the  first,  and  as  the  strength  also  gets  nearer  and  nearer  to 
that  point  where  the  vapor  tension  is  negligable,  the  percentage 
absorbtion  is  increasingly  great,  and  if  the  acid  in  all  towers  is 
above  the  dead  line  of  98.3  per  cent,  so  that  no  "mist"  is  formed, 
the  absorbtion  will  be  practically  complete. 

The  use  to  which  the  acid  is  to  be  put  of  course  determines  the 
strength  to  be  made,  but  the  season  of  the  year  has  an  influence 
also:  and  a  look  at  the  freezing  curve,  in  Chapter  XXIII,  will 


240 


AMERICAN  SULPHURIC  ACID  PRACTICE 


show  why.  Acid  of  about  103.6  per  cent  with  a  freezing  point 
of  10°F.  is  a  good  winter  strength  to  aim  at. 

While  analysis  is  necessary  to  determine  the  strength  of  acid 
in  the  various  towers,  experience  will  soon  teach  the  operator 
how  often  to  sample:  and  while  this  system  is  very  flexible,  and 
will  stand  a  lot  of  bad  handling,  it  is  easy  to  handle  well. 

If  the  Feld  washer,  made  by  the  Bartlett-Hayward  Co.,  of 
Baltimore,  can  be  designed  to  stand  fuming  acid  it  will  be  an 
ideal  piece  of  apparatus,  and  as  the  rotating  part  is  hung  from 
an  overhead  bearing,  out  of  the  acid,  it  seems  reasonable  to  hope 
that  it  will.  Of  course  there  is  bound  to  be  some  vibration, 
which  in  time  is  sure  to  open  up  the  joints  in  the  acid  lining. 


Cooling  Coil -e^P/pe* 


FIG.  78. 

It  has  been  proposed  to  build  the  tower  of  stone-ware,  but  this 
seems  impracticable  to  the  writer,  because  of  the  high  tempera- 
tures in  the  first  towers,  which  would  be  reasonably  sure  to 
crack  the  stone-ware  if  a  draft  of  cold  air  struck  the  outside. 

Apparatus  of  the  type  shown  in  the  cut  on  this  page 
is  very  satisfactory.  The  pump  is  a  centrifugal,  made  by 
G.  C.  Bretting,  Ashland,  Wis.,  belt  driven,  1700  R.P.M.,  deliver- 
ing 40  cu.ft.  of  acid  a  minute,  and  requiring  7J/£  H.P.  It  is 
built  with  a  manhole  cover,  so  can  be  hoisted  into  place  by  a 
chain  block  on  a  mono-rail,  and  fastened  with  set  screws.  As  the 
pump  is  about  the  only  part  of  the  system  that  is  likely  to  get  out 
of  order,  this  ease  in  changing  is  very  important.  The  pump 
made  by  the  Kutztown  Foundry  &  Machine  Co.,  Kutztown,  Pa., 
is  also  a  good  one. 


ABSORBTION 


241 


Failures  of  the  wrought  iron  piping  come  apparently  not  from 
corrosion,  but  from  bursting.  These  bursts  are  always  longi- 
tudinal, and  can  be  welded.  The  writer  has  seen  many  bursts, 
but  never  one  on  a  welded  pipe,  either  at  the  weld  or  anywhere 


_n 


Section  A-6 


else  in  that  vicinity,  which  seems 
to  show  that  when  the  internal 
strains  have  been  relieved  by  the 
springing  open  of  the  pipe  in  the 
first  burst,  the  acid  alone  cannot 
burst  it. 

Failure  to  provide  for  expansion 
in  pipes  handling  the  hot  acid 
from  the  tanks  is  sure  to  result  in 
broken  fittings,  as  the  acid  is  so  hot 
that  expansion  is  considerable. 

There  are  more  likely  to  be 
" spills"  of  acid  in  this  department  than  in  any  other,  so  the  floor 
must  be  one  that  will  stand  such  acid.  Common  red  brick,  laid 
dry  in  sand,  makes  a  splendid  floor. 

The  gas  coming  from  the  converters  is  hot.     The  heat  is  used 
in  the  Badische  system  to  heat  up  the  incoming  gases,  but  in 


FIG.  79. — Distributor  plate  for 
tower. 


FIG.  80. — Converters. 

the  Schroeder-Grillo  process  the  heat  must  be  removed  by  some 
other  means.  The  simplest  means  is  a  cast  iron  or  steel  header, 
with  6-in.  wrought-iron  pipe  running  to  another  header.  For  our 
standard  unit  450  ft.  of  6-in.  pipe  will  do  the  work,  without 

16 


242  AMERICAN  SULPHURIC  ACID  PRACTICE 

help  in  winter,  but  will  require  the  help  of  a  spray  of  water  in  the 
summer. 

Drainage  must  be  allowed  for  in  the  bottom  of  the  cooler,  as 
no  matter  how  well  the  mass  is  made  up  the  magnesium  sulphate 
is  sure  to  contain  some  moisture,  which  of  course  will  form  acid 
and  condense  in  the  cooler.  This  blocks  the  system. 

The  ''absorber  man"  has  little  to  do  but  sample  and  shift  his 
acid,  as  it  increases  in  strength,  and  could  easily  handle  four 
absorber  units;  so  where  the  production  is  sufficient  it  is  custom- 
ary to  house  two  units  in  the  same  building,  in  parallel.  Weak 
acid  is  usually  received,  and  strong  delivered,  at  this  end. 


CHAPTER  XXI 
CONVERTER  MASS 

The  most  costly  part  of  a  contact  plant  is  the  platinum,  and 
every  effort  is  being  made  to  find  a  suitable  substitute,  and  failing 
that,  to  reduce  the  amount  necessary.  As  the  catalytic  action  is 
undoubtedly  a  surface  condensation,  the  logical  thing  to  do  is  to 
spread  the  platinum  out  as  thin  as  possible.  Much  research 
work  has  been  done  along  these  lines. 


FIG.  81. 

As  with  varying  conditions  it  is  not  possible  to  use  any  stand- 
ard plant,  a  simple  laboratory  converter  is  useful,  and  will  be 
here  described. 

Five  (5)  2-in.  C.I.  tees,  connected  by  close  nipples,  and  a 
2  X  6-in.  flange  at  the  outlet,  on  another  close  nipple,  the  whole 
stood  upright,  and  a  circle  of  10  mesh  iron  wire  screen  resting 

243 


244  AMERICAN  SULPHURIC  ACID  PRACTICE 

in  the  bottom  of  each  tee,  upon  the  upper  end  of  the  close  nipple. 
The  mass  is  put  in  through  the  outlet,  held  from  running  out  by 
a  piece  of  screen  sprung  in,  the  companion  flange,  in  which  there  is 
a  %  X  2-in.  bushing,  put  on,  the  therihometer  put  in  the  bushing, 
connected  up  with  the  gas  supply  at  the  lower  end,  and  started  off. 
Plastic  asbestos  is  the  best  covering,  and  such  a  system  must 
be  covered,  as  the  area  is  large  in  proportion  to  the  volume. 
(Fig.  81.) 

Sodium  free  magnesium  sulphate  is  melted  in  its  water  of 
crystalization  (it  contains  52  per  cent)  in  a  crucible,  stirring  con- 
tinuously after  it  melts,  both  to  prevent  its  sticking  and  to  make 
it  porous — the  porosity  depends  directly  upon  the  amount  of 
stirring.  In  about  35  min.  the  mass  will  be  free  from  water  and 
solidifies,  when  it  is  heated  to  a  dull  red,  and  poured  out  to  cool. 
After  cooling  it  is  broken  to  pass  a  %-in.  screen,  but  to  stay  on  a 
J^-in.  one.  The  platinic  chloride  is  then  sprayed  on  with  a  glass 
nozzle,  from  a  solution  made  up  as  later  described  in  this  chapter, 
the  mass  put  back  in  the  furnace  in  the  crucible  and  heated  to  a 
dull  red,  when  the  chloride  is  reduced  to  metallic  platinum  and  the 
mass  turns  black.  It  is  then  ready  for  use. 

Such  a  plant  will  enable  the  research  laboratory  to  work  out 
any  problems  in  connection  with  the  gas  to  be  used. 

PREPARATION  OF  MASS 

Platinum  has  increased  in  price  within  the  last  eight  years,  up 
to  1920,  from  $12  to  $145  a  Troy  ounce,  and  as  the  quantity 
necessary  to  get  a  97  per  cent  conversion,  in  a  plant  burning  12 
tons  of  sulphur  a  day  of  24  hours,  is  about  1,300  oz. — $188,500 
— every  effort  must  be  made  to  spread  it  out  very  thin. 

The  logical  thing  to  do  is  to  deposit  it  upon  a  base  of  such 
uneven  surface  that  a  very  large  area  is  exposed  in  a  relatively 
small  volume.  This  base  must  also  be  unaffected  by  the  gases 
passing  through,  by  the  temperature,  and  by  the  chemicals  used 
in  depositing  the  platinum.  It  should  also  be  of  such  a  nature 
that  the  platinum  can  be  easily  recovered. 

Asbestos  fibre  fulfills  perfectly  the  first  four  requirements,  and 
is  largely  used.  It  has  the  fault  of  packing  under  any  consider- 
able weight,  so  the  converter  must  have  shelves  only  a  few  inches 
apart,  thus  having  comparitively  shallow  layers  of  platinized 
asbestos. 


CONVERTER  MASS  245 

Dehydrated  magnesium  sulphate  answers  all  five  requirements, 
plus  the  fact  that  it  does  not  pack. 

The  base  is  coated  by  spraying  with  a  solution  of  platinic 
chloride,  made  by  dissolving  platinum  at  the  rate  of  125  gr.  Pt 
per  liter  beaker  in  twice  the  theoretical  amount  of  aqua  regia. 
This  is  heated  over  a  sand  bath.  The  beaker  should  stand  in  a 
porcelain  dish  containing  water,  large  enough  to  hold  the  entire 
contents  of  the  beaker,  in  case  of  accident. 

About  80  per  cent  of  the  platinum  will  dissolve  readily.  This 
solution  is  poured  into  a  porcelain  dish,  which,  for  safety's  sake, 
stands  inside  a  larger  dish,  and  is  concentrated.  More  aqua 
regia  is  added  to  the  undissolved  portion,  until  all  has  gone  into 
solution. 

The  solution  is  then  analyzed  and  diluted  to  contain  7  gr.  per 
c.c.*  Because  of  the  high  atomic  weight  of  solutions  containing 
platinum,  they  diffuse  slowly,  so  mixing  must  be  very  carefully 
and  thoroughly  done.  This  is  diluted  to  Jf  Q  before  using. 

The  asbestos  fibre  must  be  very  carefully  "fluffed,"  and  the 
solution  sprayed  on  from  glass  bottles,  through  a  rubber  tube 
with  a  glass  nozzle,  drawn  to  a  fine  opening,  using  low-pressure 
air  to  drive  the  solution  out.  The  asbestos  must  be  turned  over 
continually,  to  get  as  even  a  distribution  as  possible :  a  pitchfork 
makes  a  good  tool. 

This  mass  is  put  right  into  the  converters,  where  the  heat  of 
starting  up  reduces  the  platinic  chloride  to  metallic  platinum 
before  the  first  862  arrives  for  conversion. 

The  magnesium  sulphate  used  must  be  pure.  The  New  Jersey 
Zinc  Co.  supplies  a  very  high  grade. 

A  small  reverberatory  furnace  is  used  for  calcining  the  "mag. 
sulph."  lots  of  250  Ib.  to  500  Ib.  being  a  charge.  Thirty-five  to 
40  min.  is  sufficient  time  to  melt  the  salt  in  its  own  water  of 
crystallization  and  drive  the  water  off.  The  furnace  should  be  at 
a  dull  red  heat,  and  the  charge  rabbled  continuously,  as  otherwise 
it  will  harden  and  stick  to  the  hearth.  The  more  it  is  rabbled 
the  more  porous  it  becomes. 

*  The  Avoirdupois  pound  is  the  usual  unit  of  weight  in  the  sulphuric  acid 
industry,  but  platinum  is  weighed  in  the  Troy  (or  Jewelers')  scale.  The 
following  comparisons  of  the  two  scales  are  helpful: 

1  pound  Avoirdupois  =  7,000  grains  =  16  Avoirdupois  ounces, 
1  pound  Troy  =  5,760  grains  =  12  Troy  ounces. 

1  pound  Troy  =  .8229  pounds  Avoirdupois. 


246  AMERICAN  SULPHURIC  ACID  PRACTICE 

After  the  charge  is  drawn  it  is  broken  and  screened,  pieces 
above  %  in.  being  broken,  and  below  >£  in.  rejected. 

Various  plants  use  varying  amounts  of  platinum  per  unit  of 
mass — 0.2  per  cent  to  0.3  per  cent  are  the  most  usual. 

The  spraying  is  done  the  same  as  with  asbestos  fibre,  but  the 
mass  is  put  back  into  the  furnace  for  20  or  30  min.,  at  a  dull  red 
.heat,  and  rapidly  turns  black,  from  the  reduction  of  platinic 
chloride. 

REGENERATION 

Asbestos  is  difficult  to  dissolve,  so  when  it  is  necessary  to 
recover  the  platinum  it  is  simpler  to  dissolve  the  platinum  in  aqua 
regia,  filter,  purify  the  solution,  and  make  new  mass,  than  to  try 
to  dissolve  the  asbestos. 

A  spraying  with  a  solution  containing  20  per  cent  HC1,  7  per 
cent  HN03,  and  a  little  soluble  organic  matter,  such  as  starch  or 
sugar,  and  returning  the  mass  to  the  converter,  will  serve  for 
regeneration  if  the  mass  is  not  in  very  bad  shape.  The  effect 
is  to  dissolve  (partially)  and  redistribute  the  platinum,  and  dis- 
solve the  impurities  and  have  them  carried  off  in  the  gases  from 
the  burning  organic  matter. 

If  the  mass  from  magnesium  sulphate  to  be  regenerated  con- 
tains a  large  proportion  of  fines  it  should  be  put  into  a  wooden 
tub,  with  a  solution  similar  to  that  used  for  ordinary  regenera- 
tion, and  water  added  as  the  solution  boils  down  from  the  heat 
of  the  reactions;  and  finally,  after  perhaps  10  to  24  hours,  a 
smooth  paste  results.  It  should  be  more  or  less  sloppy.  The 
finer  the  material  the  less  time  required. 

The  result  is  a  semi-solution  of  crystalline  magnesium  sulphate, 
with  platinum,  which  is  furnaced  as  was  the  new  salt,  and  the 
mass  is  then  ready  for  use. 

Of  course  this  treatment  results  in  some  platinum  being  shut 
up  within  the  pieces  of  magnesium  sulphate,  and  the  action  of 
such  quantities  lost,  so  it  is  good  practice  to  spray  on  5  per  cent 
of  the  original  quantity,  after  regeneration.  After  several 
regenerations  the  salt  should  be  dissolved  in  a  weak  sulphuric 
acid  solution,  the  platinum  recovered,  and  new  mass  made. 


CHAPTER  XXII 

ACCOUNTING 
BY  W.  M.  LE  CLEAR 

All  well  organized  concerns  recognize  the  advantages  of  Cost 
Sheets  which  reflect  the  costs  to  a  very  accurate  degree,  and  it 
is  not  considered  necessary  to  dwell  or  argue  upon  this  point, 
because  it  is  a  conceded  fact  that  without  these  records  the 
management  cannot  follow  the  destinies  of  its  operations. 

The  usual  factors  entering  into  the  cost  of  any  product  are 
appraised  here — i.e. 

Labor,  direct,  Repairs  and  Maintai  nance, 

Labor,  indirect,  Insurance,  Taxes,  etc., 

Materials,  direct,  Overhead, 

Materials,  indirect,  Depreciation. 

These  various  charges  reflected  in  the  cost  sheets  may  come 
through  sub-cost  sheets,  such  as  Power  House  cost  sheets,  or 
they  may  be  charged  direct  to  the  Sulphuric  Acid  cost  sheet, 
depending  entirely  upon  what  basis  the  managment  wishes  the 
cost  data  to  be  prepared.  In  either  case  the  final  result  should 
be  identical. 

The  Direct  Labor  represents  the  labor  actually  employed  in 
obtaining  the  product.  The  Indirect  Labor  is  labor  that  is 
necessary  to  the  operation,  but  which  does  not  go  directly  into 
the  product,  as  for  instance,  foremans'  time,  laboratory  time, 
sweepers,  oilers,  etc., 

Direct  and  Indirect  Materials  are  classified  along  lines  similar 
to  the  Direct  and  Indirect  Labor.  Direct  Materials  represent 
such  items  as  sulphur,  pyrites,  etc.,  while  the  Indirect  Materials 
would  be  Nitric  acid  in  some  form  (usually  Chile  saltpeter), 
fuel  etc. 

The  Repair  and  Maintainance  charges  should  represent  the 
labor  and  materials  expended  which  skeep  the  apparatus  in 
operating  condition,  and  do  not  add  perceptably  to  the  life  of  the 

247 


248  AMERICAN  SULPHURIC  ACID  PRACTICE 

equipment.  Charges  falling  into  the  latter  classification  should 
be  capitalized. 

The  Charges,  for  Taxes,  Insurance,  etc.,  should  be  determined 
as  nearly  as  is  possible  to  estimate  them.  It  may  not  be  amiss 
to  state  that  accounting  authorities  do  not  consider  the  United 
States  Government  Income  and  Excess  Profits  Taxes  to  be  a 
part  of  the  manufacturing  cost,  and  are  in  reality  a  division  of 
profits  with  the  Government. 

The  charge  for  Depreciation  should  represent  the  diminish- 
ment  in  value  due  to  wear,  tear,  and  obsolesence,  as  nearly  as  it 
can  be  estimated.  With  proper  care  the  buildings  will  last  a 
long  time,  while  the  chambers,  the  most  costly  part  of  a  chamber 
plant,  should  be  amortized  on  an  8-year  basis,  although  they 
will  frequently  go  10.  Other  parts  of  the  plant  must  be  taken 
care  of  with  regard  to  their  varying  life.  The  thought  I  wish  to 
bring  out  is  that  no  one  figure  will  do  for  a  plant  making  corrosive 
chemicals.  Buildings  at  4  per  cent  and  Power  House  Equipment 
at  10  per  cent,  will  fit  in  very  well. 

The  charges  for  Overhead  should  represent  General  Office 
salaries,  etc.,  which  are  not  charged  under  the  classifications 
rreviously  discussed.  If  desired  the  details  on  the  cost  sheets 
may  be  carried  out  to  the  minutest  details,  but  ordinarially 
this  is  not  considered  necessary. 

The  basic  feature  to  be  borne  in  mind  in  the  preparation  of 
the  Cost  Sheet  is,  that  EVERY  CHARGE  that  has  any  bearing 
upon  costs  is  reflected  therein.  The  details  of  these  items  and 
their  arrangement  is  of  course  important,  but  only  secondarily 
so. 

It  is  probably  unnecessary  to  add  that  the  costs  should  be 
reflected  upon  the  pounds  of  100  per  cent  acid  produced. 

It  is  difficult  to  lay  down  any  specific  rules  or  instructions 
regarding  the  cost  information  which  should  be  furnished  daily, 
as  this  feature  depends  entirely  upon  what  the  management 
considers  necessary  for  its  information.  It  is  very  important 
however  that  the  management  know  the  number  of  men,  cost  of 
labor  and  materials  used,  and  the  production  daily.  The 
author's  opinion  is  that  all  elements  of  cost  should  be  calculated 
daily,  some  factors  must  of  necessity  be  estimated,  which  by 
the  preparation  of  a  monthly  progressive  sheet  would  at  the 
end  of  each  month  very  closely  tie  up  with  the  monthly  cost 
sheet. 


ACCOUNTING  249 

Per  1,000  Ib.  H2SO4 

Labor 1.3 -hr.  @  48c. 

(Production  roughly  3,825,000  Ib.  per  mo.) 

Say  $275,000.00  investment  per  line. 

Interest  6  per  cent 16,500 

Dep.  25  per  cent 68,750 

Insurance  3  per  cent 8,250 

Taxes  1.5  per  cent 4,125 

$97,625 

Labor 624 

Materials,  330  Ib.  S 3.03 

Coal 50 

Superintendence 16 

Office  and  labor  including  supplies 075 

Capital 2.12 

$6.509 

Repairs  not  included. 

Steam  not  included. 


APPENDIX 
TANK  CAR  TABLE 

The  Standard  Tank  Car  for  acid  is  78  in.  in  diameter,  and  the 
length  of  the  side  is  27  ft.  6  in.     The  two  ends  are  dished  OUt- 
Depth,  Per Cent 


1 

45 

40 

Tt 

30     95       90       85       80       75       70       66       SO       55      5C 

30 
55 

r  A 

/ 

• 

/ 

r 

x 

z 

65 

T5 
80 

90 
95 
100 

// 

x 

S 

\\ 

/ 

/ 

1 
|ZO 

10 
5 
0 

.VV] 

1 

r? 

/ 

2 

/ 

/ 

x 

x 

/ 

? 

^ 

<1 

^ 

10        15       EO       25       30       J5       40       45      50 
Depth,  Per  Cent 


NOTE 

Curve  "A  "=  %  P<?;?tf7  V5.  %  Contents  Curve  for  Plainfylinder, 

Longitudinal  /Ixis  Horizontal 

Curve  "B"-  %  Depth  vs.  %  Contents,  Curve  for  Dished  End 
Total  Volume  of  Cylinder  Referred  to  inCurve"A"<=O.7854D*L 
Total  Volume  of^  Ends,  Refer  red  to  in  Curve  "8"=27th2(D-tl) 

In  Which;  =.I0774D3* 

0  -Inside  Diameter'  of  Tank^  and  Radius  of  Dished  End 
L  -  Length  of  Plain  Cylindrical  Part  of  Tank 
h  =  Toraf  Depth  of  Di&hed  End 


FIG.  82. 

wards,   the  radius  of   the  dish  always  being  the  same  as  the 
diameter  of  the  tank  itself. 

250 


APPENDIX  251 

Other  sizes  of  "tanks"  are  used  for  acid — so  many  in  fact 
that  it  would  be  out  of  the  question  to  give  a  gaugeing  table  for 
all  sized  tanks.  However,  with  the  tank  curve  a  table  for 
any  sized  tank  can  be  quickly  prepared. 

To  prepare  such  a  table,  first  find  the  area  of  the  vertical 
section  of  the  car  in  feet:  then  multiply  this  by  the  length  of 
the  straight  side  of  the  tank — this  will  give  you  the  number  of 
cubic  feet  in  the  cylindrical  part  of  the  tank.  Then  prepare  a 
table  giving  the  per  cent  of  height  for  every  inch  of  height — then 
set  down  opposite  each  inch  the  per  cent  of  the  capacity  of  the 
tank  that  is  represented  at  that  height — for  instance,  in  the 
table  given,  at  16  in.  the  per  cent  of  the  total  is  20.54.  Then 
multiply  this  by  913+ ,  which  is  what  the  cylinder  holds  full, 
and  you  get  135.55  cu.  ft.  Then  figure  from  the  formula  given 
how  much  the  dished  ends  hold  full,  look  on  the  "end  curve" 
to  see  how  much  the  ends  hold  at  20.54  per  cent,  and  you  will 
find  it  is  about  8.4  per  cent.  From  the  formula  the  ends  hold 
about  37  cu.  ft.,  and  you  get  3.08  cu.  ft.,  which  added  to  the 
135.55  cu.  ft.  of  the  cylinder  gives  you  the  amount  of  acid  in 
the  tank:  138.63  cu.  ft. 

Because  of  the  varying  relations  between  the  length  and 
diameter,  it  is  not  possible  to  work  it  all  out  in  one  formula, 
so  a  table  must  be  prepared  as  above. 

From  a  hydrometer  the  density  of  the  acid  is  then  determined, 
its  weight  per  cu.  ft.  looked  up,  and  the  total  weight  calculated. 

While  there  may  be  some  errors  in  the  last  place  of  decimals, 
it  is  not  possible  to  read  a  stick  to  within  one-hundredth  of  an 
inch,  and  after  a  tank  car  has  been  in  service  a  very  short  time 
it  will  be  distorted  more  than  any  error  in  this  curve. 


252  AMERICAN  SULPHURIC  ACID  PRACTICE 

TABLE  FOR  STANDARD  TANK  CAR 


Height 
of  acid 
in  tank, 
inches 

Per  cent  of 
depth 

No.  of 
cu.  ft. 

Height 
of  acid 
in  tank, 
inches 

Per  cent  of 
depth 

No.  of 
cu.  ft. 

1 

1.28 

2.24 

40 

51.28 

491  .  02 

2 

2.56 

6.09 

41 

52.56 

506.96 

3 

3.84 

11.67 

42 

53.84 

523.58 

4 

5.13 

17.88 

43 

55.13 

538.10 

5 

6.41 

24.81 

44 

56.41 

553.55 

6 

7.69 

32.49 

45 

57.69 

569.00 

7 

8.98 

40.93 

46 

58.98 

584  .  42 

8 

10.26 

49.85 

47 

60.26 

599.73 

9 

11.54 

59.36 

48 

61.54 

615.17 

10 

12.83 

68.52 

49 

62.83 

630.28 

11 

14.11 

79.23 

50 

64.11 

645.33 

12 

15.38 

90.65 

51 

65.38 

660.29 

13 

16.69 

102.32 

52 

66.69 

675  .  20 

14 

17.97 

114.07 

53 

67.97 

689.72 

15 

19.25 

126.24 

54 

69.25 

704.14 

16 

20.53 

138.63 

55 

70.54 

718.71 

17 

21.82 

150.97 

56 

71.82 

732.95 

18 

23.10 

163.31 

57 

73.10 

746.74 

19 

24.39 

176.43 

58 

74.39 

760.22 

20 

25.67 

189.78 

59 

75.67 

773.57 

21 

26.95 

203.26 

60 

76.95 

786.69 

22 

28.24 

217.05 

61 

78.24 

799.03 

23 

29.52 

231.29 

62 

79.52 

811.37 

24 

30.80 

245.86 

63 

80.80 

823.76 

25 

32.09 

260.28 

64 

82.09 

835.93 

26 

33.37 

274.80 

65 

83.37 

847.68 

27 

34.65 

289.71 

66 

84.65 

859.35. 

28 

35.93 

304.67 

67 

85.93 

870.77 

29 

37.21 

319.72 

68 

87.21 

881.48 

30 

38.49 

334.83 

69 

88.49 

890.64 

31 

39.77 

350.27 

70 

89.77 

900.15 

32 

41.05 

365.58 

71 

91.05 

909.07 

33 

42.33 

381.00 

72 

92.33 

917.51 

34 

43.62 

396.45 

73 

93.61 

925.19 

35 

44.89 

411.90 

74 

94.89 

932.12 

36 

46.17 

427.42 

75 

96.17 

938.33 

37 

47.45 

443.04 

76 

97.45 

943.91 

38 

48.72 

458.98 

77 

98.73 

947.46 

39 

50.00 

475.  00  half  full 

78 

100.00 

950.00 

APPENDIX 


253 


Tables  and  General  Information 

SPECIFIC  GRAVITY 
Manufacturing  Chemists  Association  of  the  United  States 


°Be\ 

Sp.  gr. 

Per  cent 
H2SO4 

Weight  of 
1  cu.  ft.  in 
pounds,  av. 

Freezing 
(melting) 
point,  °F. 

0 

1.0000 

0.00 

62.37 

32.0 

1 

1  .  0069 

1.02 

62.80 

31.2 

2 

1.0140 

2.08 

63.24 

30.5 

3 

1.0211 

3.13 

63.69 

29.8 

4 

1.0284 

4.21 

64.14 

28.9 

5 

.0357 

5.28 

64.60 

28.1 

6 

.0432 

6.37 

65.06 

27.2 

7 

.0507 

'  7.45 

65.53 

26.3 

8 

.0584 

8.55 

66.01 

25.1 

9 

.0662 

9.66 

66.50 

24.0 

10 

.0741 

10.77 

66.99 

22.8 

11 

.0821 

11.89 

67.49 

21.5 

12 

1  .  0902 

13.01 

68.00 

20.0 

13 

1.0985 

14.13 

68.51 

18.3 

14 

1  .  1069 

15.25 

69.04 

16.6 

15 

1.1154 

16.38 

69.57 

14.7 

16 

1.1240 

17.53 

70.10 

12.6 

17 

1  .  1328 

18.71 

70.65 

10.2 

18 

1.1417 

19.89 

71.21 

7.7 

19 

1.1508 

21.07 

71.78 

4.8 

20 

1.1600 

22.25 

72.35 

1.6 

21 

1.1694 

23.43 

72.94 

-   1.8 

22 

1.1789 

24.61 

73.53 

-  6.0 

23 

1.1885 

25.81 

74.13 

-11.0 

24 

1.1983 

27.03 

74.74 

-16.0 

25 

1.2083 

28.28 

75.36 

-23.0 

26 

1.2185 

29.53 

76.00 

-30.0 

27 

1.2288 

30.79 

76.64 

-39.0 

28 

1.2393 

32.05 

77.30 

-49.0 

29 

1.2500 

33.33 

77.96 

-61.0 

30 

1.2609 

34*63 

78.64 

-74.0 

31 

1.2719 

35.93 

79.33 

-82.0 

32 

1.2832 

37.26 

80.03 

-96.0 

33 

1  .  2946 

38.58 

80.74 

-97.0 

34 

1.3063 

39.92 

81.47 

-91.0 

35 

1.3182 

41.27 

82.22 

-81.0 

36 

1.3303 

42.63 

82.97 

-70.0 

37 

1.3426 

43.99 

83.74 

-60.0 

254  AMERICAN  SULPHURIC  ACID  PRACTICE 

SPECIFIC  GRAVITY 
Manufacturing  Chemists  Association  of  the  United  States 


°Be\ 

,     Sp.  gr. 

Per  cent 
H2SO4 

Weight  of 
1  cu.  ft.  in 
pounds,  av. 

Freezing 
(melting) 
point,  °F. 

38 

1.3551 

45.35 

84.52 

-53 

39 

1.3679 

46.72 

85.32 

-47 

.40 

1.3810 

48.10 

86.13 

-41 

41 

1.3942 

49.47 

86.96 

-35 

42 

1  .  4078 

50.87 

87.80 

-31 

43 

.4216 

52.26 

88.67 

-27 

44 

.  4356 

53.66 

89.54 

-23 

45 

.4500 

55.07 

90.44 

-20 

46 

.4646 

56.48 

91.35 

-14 

47 

.4796 

57.90 

92.28 

-15 

48 

.4948 

59.32 

93.23 

-18 

49 

.5104 

60.75 

94.20 

-22 

50 

.5263 

62.18 

95.20 

-27 

51 

.5426 

63.66 

96.21 

-33 

52 

.5591 

65.13 

97.24 

-39 

53 

.5761 

66.33 

98.30 

-49 

54 

.5934 

68.13 

99.38 

-59 

55 

.6111 

69.65 

100.48 

Below  -40 

56 

1.6292 

71.17 

101.61 

Below  -40 

57 

1.6477 

72.75 

102.77 

Below  -40 

58 

1.6667 

74.36 

103.95 

Below  -40 

59 

1.6860 

75.99 

105.16 

-  7 

60 

1.7059 

77.67 

106.40 

+  12.6 

61 

1.7262 

79.43 

107.66 

27.3 

62 

1.7470 

81.30 

108.96 

39.1 

63 

1.7683 

83.34 

110.29 

46.1 

64 

1.7901 

85.66 

111.65 

46.4 

64K 

1.7057 

86.33 

112.00 

43.6 

64** 

1.8012 

87.04 

112.34 

41.1 

64% 

1.8068 

87.81 

112.69 

37.9 

65 

1.8125 

88.65 

113.05 

33,1 

65H 

1.8182 

89.55 

113.40 

24.6 

65^ 

1.8239 

90.60 

113.76 

-f-13.4 

65% 

1.8297 

91.80 

114.12 

-   1.0 

66 

1.8354 

93.19 

114.47 

-29.0 

APPENDIX  255 

ALLOWANCE  FOR  TEMPERATURE 


At 

10 

0 

Be, 

.039° 

Be. 

or 

.  00023 

sp. 

gr. 

= 

•1    ( 

At 

20 

0 

Be, 

.036° 

Be\ 

or 

.  00034  sp. 

gr. 

= 

1    C 

At 

30 

0 

Be, 

.035° 

Be. 

or 

.00039 

sp. 

gr. 

= 

1' 

At 

40 

0 

Be, 

.031° 

Be\ 

or 

.00041 

sp. 

gr. 

a 

1 

At 

50 

0 

Be, 

.028° 

Be\ 

or 

.00045 

sp. 

gr. 

= 

1 

At 

60 

o 

Be, 

.026° 

Be\ 

or 

.  00053 

sp. 

gr. 

= 

1 

At 

63 

°Be\,   .026°Be*. 

or 

.00057 

sp. 

gr. 

= 

1 

At66°Be.,   .023£ 

i°Be. 

or 

.  00054 

sp. 

gr. 

a 

1 

APPROXIMATE  BOILING  POINTS 

50°B6 295°F.  63°Bd 432°F. 

60°Be 386°F.  64°Be 451°F. 

61°Be 400°F.  65°B6 485°F. 

62°B^..  .  415°F.  66°B^ 538°F. 


THEORETICAL  PRODUCTION  FIGURE 
=  3.0585  Log  of  3.0585  =  .485508 


SPECIFIC  GRAVITY  (AT  95°F.)  AND  MELTING  POINT  (FREEZING  POINT)  OF 
FUMING  SULPHURIC  ACID 

TOTAL  803                   FREE  Soa  SP.  OR.  MELTING  (FREEZING) 

POINT,  °F. 

81.63                     0.00  1.8136  50.0 

82  2.05  1.8300  46.7 

83  7.50  1.8480  31.5 

84  12.95  .8657  14.5 

85  18.38  .8847  12.2 

86  23.84  .9086  28.1 

87  29.27  .9258  56.3 

88  34.70  .9429  78.8 

89  40.17  .9607  93.6 

90  45.63  .9667  93.6 


256 


AMERICAN  SULPHURIC  ACID  PRACTICE 


PER  CENT     TOTAL  SOa  WHEN  FREE  SOs  = 


PER  CENT  TOTAL  SOa  WHEN  FREE  SO» 


81.63 

00 

81.99 

2 

82.36 

4 

82.73 

6 

83.09 

8 

83.46 

10 

83.82 

12 

84.20 

14 

84.66 

16 

84.93 

18 

85  ..30 

20 

85.66 

22 

86.03 

24 

86.40 

26 

86.76 

28 

87.14 

30 

87.50 

32 

87.87 
88.24 
88.60 
88.97 
89.33 
89.70 
90.07 
90.44 
90.81 
91.18 
91.55 
91.91 
92.28 
92.65 
93.02 
93.38 
93.75 


34 
36 
38 
40 
42 
44 
46 
48 
50 
52 
54 
56 
58 
60 
62 
64 
66 


TOTAL  SO» 

PER  CENT 

80 

82 

84 

86 

88 

90 

PER  CENT 

36°F. 

H2SO4 

M.M. 

61.7 

3 

70.0 

2 

81.5 

1 

89.0 

0 

Above  90.0 

Oat 

SPECIFIC  HEAT 
SPEC.  HEAT          TOTAL  SOs  PER  CENT 


.3500 
.3450 
.3400 
.3390 
.3500 
.3600 


92 
94 
96 
98 
100 


VAPOR  TENSION 

104°F.  140°F. 

M.M.  M.M. 

10  25 

3  8 

1  1.5 

0  0 
0  at  all  temperature. 


176°F. 

M.M. 

68 
22 

3 

0 


SPEC.  HEAT 

.4000 
.4550 
.5350 
.6500 

.7700 


212°F. 

M.M. 

143 

57 

10 

1 


APPENDIX 


257 


VAPOR  PRESSURES  OF  SOME  QUALITIES  OF  OLEUM 
Y±  volume  oleum.     y±  volume  air. 


Pres- 

Pres- 

Pres- 

Pres- 

Pres- 

Pres- 

Pres- 

Temp. 

sure  of 

sure  of 

sure  of 

sure  of 

sure  of 

sure  of 

sure  of 

°C. 

oleum, 

oleum, 

oleum, 

oleum, 

oleum, 

oleum, 

oleum, 

30% 

40% 

50% 

60% 

70% 

80% 

100% 

atrn. 

atm. 

atm. 

atm. 

atm. 

atm. 

atm. 

35 

/• 

0.150 

0.40 

40 

0.075 

0.225 

0.375 

0.500 

0.65 

45 

0.050 

0.125 

0.350 

0.575 

0.650 

0.87 

50 

0.100 

0.175 

0.350 

0.525 

0.775 

0.875 

1.20 

55 

0.140 

0.225 

0.450 

0.675 

1.025 

1.200 

1.60 

60 

0.200 

0.275 

0  550 

0.825 

1.400 

1.500 

1.85 

.    65 

0.225 

0.350 

0.700 

1.025 

1.650 

1.900 

2.25 

70 

0.275 

0.400 

0.825 

1.275 

2.050 

2.300 

2.75 

75 

0.340 

0.475 

1.000 

1.570 

2.525 

2.800 

3.30 

80 

0.400 

0.575 

1.150 

1.850 

3.100 

3.500 

4.00 

85 

0.450 

0.675 

1.400 

2.150 

3.700 

4.175 

4.90 

90 

0.530 

0.825 

1.700 

2.575 

4.400 

5.050 

5.90 

95 

0.625 

0.950 

2.050 

3.150 

5.000 

6.000 

.... 

100 

0.730 

1.100 

2.400 

3.700 

6.000 

17 


258          AMERICAN  SULPHURIC  ACID  PRACTICE 

HEAT  OF  SOLUTION.     (DR.  KNEITCHE) 

Determined  Values 
HiSO«  PER  CENT         SOi  PER  CENT        FREE  SOi  PER  CENT          CALORIES 

60.32                    41.07                    40.45 

60.18                    49.12                    65.46 

63.86                    52.13                    79.05 

70.24                    57.33                    110.05 

73.76                    6021                    132.3 

76.86                    62.74                    V 151.4 

71.41                    64.82                    171.7 

99.88                    81.62                      0.0  194.06 

'  83.49                     10.12  221.4 

85.26                    19.75  245.27 

87.31                    30.91  277.6 

89.08                     40.55  299.05 

91.05                    51.28  327.9 

.....                     92.67                    60.10  361.4 

94 . 72                    71 . 26  393 . 6 

96.62                    81.60  433.5 

98.48                    97.81  470.6 

99.64                     99.48  491.1 

HEAT  OP  SOLUTION  OF  SOLID  OLEUM.     (DR.  KNEITCHE) 

Determined  Values 

TOTAL  SOs  PER  CENT           FREE  SOj  PER  CENT  CALORIES 

89.4  42.3  271.0 
90.73                             49.53  303.2 

92.5  59.2  330.4 
94.5                               70.1  369.2 
96.28                              79.75  408.8 
98.14                             97.32  436.1 
98.54                              99.34  481.4 
99.84                              99.77  486.0 


APPENDIX 


259 


HEAT  OF  SOLUTION  OF  SULPHURIC  ACID  AND  OLEUM.     (DR.  KNEITCHE) 
Graphically  Determined 


Sulphuric  acid 

Oleum 

S03,  % 

H2S04, 

% 

Cal. 

SO3,  % 

Free 
S03,  % 

Cal. 

Heat  of 
solution 
of  solid 
oleum,  cal. 

50 

61.25 

39 

82 

2 

199 

51 

62.48 

41 

83 

7.5 

210 

52 

63  .  70 

44 

84 

12.9 

223.5 

.  .  . 

53 

64.93 

46.5 

85 

18.3 

237.5 

. 

54 

66.15 

49 

86 

23.8 

250 

55 

67.38 

51.5 

87 

29.2 

265 

.  .  . 

56 

68.60 

54 

88 

34.7 

278 

. 

57 

69.83 

57 

89 

40.1 

292 

58 

71.05 

59.5 

90 

45.6 

308 

286 

59 

72.28 

62 

91 

51.0 

325 

304 

60 

73.50 

65 

92 

56.4 

344 

322 

61 

74.73 

68 

93 

61.9 

363 

340 

62 

75.95 

72 

94 

67.3 

381 

360 

63 

77.18 

75 

95 

72.8 

401 

380 

64 

78.40 

79 

96 

78.3 

421 

402 

65 

79.63 

83.5 

97 

83.7 

442 

423 

66 

80.85 

88 

98 

89.1 

465 

442 

67 

82.08 

93 

99 

94.6 

490 

463 

68 

83.30 

98  . 

100 

100 

515 

486 

69 

84.53 

103 

70 

85.75 

108 

71 

86.98 

113 

72 

88.20 

119 

73 

89.43 

126 

74 

90.65 

133 

75 

91.88 

139 

76 

93.10 

146 

77 

94.33 

152 

78 

95.55 

160 

79 

96.78 

168 

80 

98.00 

178 

81 

99.23 

188 

81.63 

100.00 

193 

260 


AMERICAN  SULPHURIC  ACID  PRACTICE 


ELECTRICAL   RESISTANCE  OF  SULPHURIC  ACID  AT  25°C. 
(DR.  KNEITCHE) 


S03,  % 

H2S04,  % 

Ohm 

S03,  % 

H2SO4,  % 

Ohm 

40.19 

49.23 

0.235 

75.19 

92.01 

0.70 

48.80 

59.79 

0.29 

76.73 

94.00 

0.72 

53.27 

65.14 

0.245 

78.15 

96.11 

0.795 

57.54 

70.55 

0.345 

78.52 

96.20 

0.79 

60.28 

73.85 

0.475 

79.55 

97.46 

0.80 

61.07 

74.82 

0.525 

80.22 

98.27 

1.10 

64.00 

78.40 

0.60 

80.98 

99.21 

1.95 

65.14 

79.80 

0.67 

81.27 

99.55 

2.2 

67.04 

82.14 

0.74 

81  .  345 

99.64 

2.7 

68.53 

83.97 

0.75 

81  .  425 

99.74 

3.5 

69.12 

84.68 

0  .  76  max. 

81  .  455 

99.78 

4.2 

70.23 

86.03 

0.745 

81.53 

99.87 

5.7 

70.84 

86.79 

0.74 

81  .  535 

99.88 

5.7 

73.40 

89.92 

0.705 

81.59 

99  .  95  monohydrate 

7  .  45  max. 

ELECTRICAL  RESISTANCE  OF  OLEUM  AT  25°C. 


Total 
S03,  % 

Free 

S03,   % 

Ohms 

Total 
S03,  % 

Free 

S03,  % 

Ohms 

81.695 

0.34 

6.15 

90.5 

45.0 

23.4 

81.74 

0.5 

5.35 

90.8 

50.0 

53.0 

82.4 

4.0 

2.43 

91.6 

54.0 

88.0 

83.44 

9.8 

2.20 

92.7 

60.3 

222.0 

84.2 

14.0 

2.15\     .   . 

93.4 

64.0 

287.0 

84.7 

16.7 

|  minimum 

94.6 

69.6 

759.0 

85.2 

19.4 

2.23 

95.4 

75.0 

1,265.0 

86.3 

25.5 

2.95 

96.35 

80.0 

4,  000.  Oat  27 

87.05 

29.5 

4.05 

96.87 

83.0 

6,  650.  Oat  32 

88.3 

36.3 

6.65 

98.16 

90.0 

61,  850.  Oat  36 

89.0 

40.2 

15.2 

APPENDIX 
ATTACKING  ACTION  UPON  IRON 


261 


Decrease  per  square  meter  per  hour  in  grams  after  72  hours  action  of  acid 
acid  at  18°-20°C.  [65°-68°F.].     (Dr.  Kneitche.) 


H2SO4,  % 

S03,   % 

Cast  iron 

Ingot  iron 

Welding  iron 

48.8 

39.9 

0.2177 

61.2 

50.0 

0.1510 



0.3032 

67.7 

55.3 

0  .  0847 

0  .  0789 

73.4 

59.9 

0.0662 

0  .  0623 

79.7 

65.0 

0.1560 

0.1159 

83.7 

68.4 

0.1388 

0.1052 

85.1 

69.5 

0.1306 



0.1034 

88.2 

72.0 

0.1636 

0.1417 

90.6 

73.9 

0.1750 

0.1339 

92.0 

75.2 

0  .  0983 

0.1040 

93.0 

75.9 

0.0736 

0.0987 

0.0855 

94.1 

77.0 

0.0723 

0.0933 

0.0708 

95.4 

77.9 

0.1274 

0.1471 

0.1209 

96.8 

79.0 

0.1013 

0.0815 

0.0988 

98.4 

80.3 

0.0681 

0.0533 

0.0655 

98.7 

80.6 

0.0583 

0.0509 

0.0570 

99.2 

81.0 

0.0568 

0.0418 

0.0504 

99.3 

81.07 

0.057 

0.042 

0.050 

99.5 

81.25 

0.060 

0.038 

0.049 

99.77 

81.45 

0.066 

0.042 

0.049 

100.0 

81.63 

0.087 

0.088 

0.076 

Total  SO3 

Free  SO3 

81.8 

0.91 

0.201 

0.393 

0.323 

82.02 

2.00 

0.190 

0.285 

0.514 

82.28 

3.64 

0.132 

0.441 

0.687 

82.54 

4.73 

0.154 

0.956 

1.075 

82.80 

7.45 

0.151 

0.566 

1.321 

83.50 

10.17 

0.079 

0.758 

1.540 

84.20 

12.89 

0.270 

1.024 

0.892 

84.62 

16  16 

0.271 

1.300 

0.758 

85.05 

18.34 

0.076 

1.988 

1.530 

86.00 

23.78 

0.070 

0.245 

0.471 

88.24 

34.67 

0.043 

0.033 

0.053 

90.07 

45.56 

0.040 

0.0X8 

0.019 

COMPOSITION  CARBON 

Cast  iron  ...................  3  .  55    per  cent, 

Ingot  iron  ....................  0.115 

Welding  iron.  .  .  .  ,  ............  0.076 


GRAPHITE 
2  .  787  per  cent. 


262 


AMERICAN  SULPHURIC  ACID  PRACTICE 


255 
250 
245 
240 
235 


D) 
•JE  210 


200 
195 


190 


0      5      IQ      15     20    25     50    35    40     45     50    55    60    65    10     15    80     85    90    95    100 

HN03,  Per  Cent 

FIQ.  83. — Boiling  points  of  nitric  acid. 


3V 

flO 

70 

I 

1 

.     £f) 

'0 

1 

y> 

1 

"c    50 

Qti 

^    ->U 

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"o  An 

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s 

xv! 

^y 

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1 

£ 

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^ 

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1 
' 

£  30 

i 

^ 

^* 

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\ 

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^ 

V 

r\\ 

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y 

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6    10 

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7 

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it  iv 

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?7    59     61     63     65    61     69     II     13     75    77     79     8!      83    85     87     39    91 
SO3, Per  Cent 

FIG.  84. — Freezing  (melting)  points  of  sulphuric  acid. 


APPENDIX 


263 


aooo 


L900 


--  F  I I  I  I  I     f     UUllw'nf\  _  (  |^  I 

w       10      ZO       1)0      40       50     60       TO      80      90      100     110 
Hydrometer     Tempcral-urG^GOdeg  F     Pound&,Gal.andcu.ft 
Degrees  Percentage 

FIG,  85. 


INDEX 


Abn-Bekr-Alrhases,  1 
Absorption,  14,  238 

best  temperature  for,  212 

heat  of  combination  of  SO3  and 
H2O,  238 

of  SO3  by  weaker  acid,  209 

strength  of  acid  for,  212 

towers,  238 

water  not  satisfactory  for,  238 
Accounting,  247 

Acid,  proper  strength  to  make,  239 
Acid  egg  (blow  case),  122,  213 
Adsorbtion,  228 
Alum,  17 

spirit  of,  1 

Aluminum  in  lead,  192 
American  Cyanimid  Company,  143 
American  makers  of  liquid  SO2,  77 
American  Smelting  &  Refining  Com- 
pany, 77 

Ammonia    as    source    of    NO    for 
chambers,  143 

analyses,  151 

oxidation-reaction,  149 

still,  147 

Anaconda  Copper  Mining  Company, 
92 

dust  chambers,  92 

large  Wedge  fan,  64 
Antimony,  contact  poison,  217 

in  lead,  193 

the  Triamphial  Car  of,  1 

to  harden  lead,  112 
Arsenic,  carried  by  mist,  207 

enemy  of  contact  process,  217 

in  entrance,  effect,  11 

in  entrance  gas,  5 

in  lead,  193 

removal  from  mass,  230 


Asbestos,  best  packing,  213 
fluffed  filter  packing,  224 
platinized,  228 

Avoirdupois    compared    with    Troy 
weights,  245 

B 

Bacon,  Dr.  Raymond  F.,  Louisiana 

sulphur,  28 
Badische  contact  process,  209-228 

converter,  228 

patents  bearing  upon,  229 
Battery  acid,  206 
Baume"  curve,  263 

hydrometer,  167 

tables,  253,  254,  255 
Benker  system,  196 
Bismuth,  effect  upon  lead,  192 
Blow  cases  (acid  eggs),  122,  213 
Bollman,  Dr.  Eric,  2 
Brimstone,  as  raw  material,  44 

burning  to  SO2,  49 
Brunner-Mond  Co.,  ammonia  still, 

147 

Buffalo   Foundry   &   Machine   Co., 
197,  198 

apparatus  for  recovering  acid, 

197,  198 
Builders  Iron  Foundry,  meters,  148 


Carbon  dioxide,  effect  upon  contact 

process,  11 
Cast  iron  not  dissolved  by  fuming 

acid,  213 
Catalytic  action  of  metallic  oxides, 

7,228 
law  of  mass  action  applied  to, 

235 
Catalyzer,  4,  5,  228 

other  than  platinum,  235 


265 


266 


INDEX 


Chalcopyrite,  45 

Chamber  plant,  reactions  in,  180 

operation,  180 
Chamber  process,  description  of,  82 

flow  sheet,  84 

outline,  8 
Chambers,  construction,  101,  102 

protecting  wind  pressure  on,  106 

volume  required,  110 
Chambers,  lead,  1,  2 

acid  must  be  concentrated,  189 

control  of  acid  strength,  186 

position  in  chamber  process,  83 
Chemists,  need  for,  209 
Chlorine,  in  the  contact  process,  11 
Circulation,  promoting  in  chambers, 
106 

Gilchrist  pipe  column,  108,  118 

multiple  tangent  system,  107 

plate  column,  108 
Clean  gas  absolutely  necessary  for 

conversion,  209,  217 
Cobalt,  4 
Combustion  chambers,  for  sulphur 

burners,  218 
Concentration,  Benker  system,  196 

bottom  firing,  191 

temperatures,  191-195 

by  cascade,  201 

by  Kalbperry  system,  207 

degree    of    depends    upon    its 
market,  212 

heat  exchangers,  193 

in  fused  silica,  200 

objection    to    direct    heat    in 
concentrating,    197 

pan,    186 

platinum  stills,  199 

top  firing,  190 

Conductivity  of  heat  by  sulphur,  40 
Contact  mass,  different  for  different 

methods,  209 
Contact  process,  4 

early  blunders,  210 

outline,  10,  207 

Conversion  of  SO2,  slide  rule  for,  236 
Converter  for  oxidizing  NH8,  145 

Badische,  229 

Schroeder  Grille,  232 


Converting  SO2  to  SO3,  228 

Coolers,  acid,  120 

Cooling,  different  methods,  209 

gases,  Badische  method,  219 

Schroeder,  Grille  method,  220 
Copper,  2 

in  lead,  193 

Costs,  by  contact  process,  212 
Cottrell  apparatus  for  dust  settling, 

86 
Cubical  expansion  of  sulphur,  39 


Davison  Chemical  Co.,  Silica  gal,  75 
liquid  SO 2,  75 
saving  SO2,  228 
De  Beauvais,  1 

Depreciation  on  contact  plant,  213 
Differences  between   Badische  and 
Schroeder-Grillo  contact 
processes,  209,  231 
Distillation  of  ferrous  sulphate,  4 
Distribution  of  acid  in  Glover's  and 

Gay  Lussac's,  13Q 
Draft,  179 

measurements,  178 
Drainage  necessary  for  coolers,  242 
Drinking  water,  clarifying,  18 
Ducktown  Sulphur,  Copper  &  Iron 

Co.,  SO2  from  blast,  65 
du  Pont  Co.,  91 
Dust  settling  apparatus,  86 

Cottrell  apparatus,  86 
chamber  with  hanging  wires,  91 
Howard,  91 
centrifugal,  92 
Anaconda  type,  92 
effect  in  contact  process,  217 
Dwight  &  Lloyd  sintering  machine, 
68 

E 

Electrical  conductivity  of  sulphur, 

39 

Ellison  draft  gauge,  178 
Exit  gas,  177 

testing,  177 
Expansion  joints  failures  with  acid, 

213 


INDEX 


267 


Fans,  159 

design  of,  160 

Ferrous  sulphate,  distillation  of,  4 
Fertilizer    industry    depends    upon 

H2S04,  17 

Filtering  material  grade   201 A   as- 
bestos, 163 
Flues,  methods  of  supporting,  164 

size  of,  163 

Foremen's  meetings,  214 
Frasch  process,  33 
Freezing,  acid,  15 

point    of    acid    as    related  to 
product,  212,  240 

curve  of,  points,  262 

point  of  acid,  255 
Frictional  electricity  of  sulphur,  39 
Fuming  acid,  4 

composition  and  uses,  17 
Fused  silica,  for  concentration,  201 

G 

Garbet,  Mr.,  1 

Gas     for     contact     process,     best 

strength,  211 
control,  235 
temperatures,  212 
Gauge  glasses  undependable,  222 
Gay  Lussac  tower,  reactions  in,  181 

description  of,  113 

packing,  114 

position  in  chamber  process, 

85 

Geber,  1 

General  Chemical  Co.,  209 
Glens   Falls   Machine  Co.,  sulphur 

burners,  49 
Glover  tower, 

as  a  concentrator,  99 

brick  for,  96 

chief  function  of,  98 

construction,  94 

description,  94 

lining  and  packing  of,  96 

position  in  chamber  process,83 

reactions  in,  181 

size  of,  100 
Gold,  4 


Harnish  &  Schroeder  process,  5 
Harrison  Bros.  &  Co.,  1 
Mr.  John,  2 
Hart  condenser,  141 
Heat    exchanger   for    concentrating 

acid,  193 

Heinz-Skinner  fan,  161 
High  silicon  irons,  141 
Holker,  4 

Hough,  Arthur,  205 
Humidity  combines  with  SO3,  8 
Hydrochloric    acid    in  the   contact 

process,  1 1 
Hydrometers,  167 


Impurities  in  gas  in  contact  process,  1 1 
Iridium,  4 
Iron,  4 

attacking   action   of   sulphuric 
acid  on,  261 


Jefferson,  President,  2 
K 

Kalbperry  Corporation,  concentrat- 
ing tower,  201 

L 

Labor  for  chamber  process,  187 

for  contact  process,  213,  214 
Landis,  W.  S.,  143 
Lead,  effect  upon  contact  process,  11, 

217 

flowing,  105 
life  of,  112 
methods  of  supporting,  95,  102, 

104 
quality  for  concentrating  pans, 

192 

specifications,  111 
weight  of  in  chambers,  102 
Lunge,  comments  on  American  prac- 
tice, 209 

plate  column,  108 
theory  of  chamber  acid,  9, 
180 


268 


INDEX 


M 

Magnesium  sulphate,  in  the  Schro- 

eder   process,    5,    228, 

265 

Manufacturers  in  the  U.  S.,  19,  27 
Mass    action,    law    of,    applied    to 

contact  action,  235 
Mass  contact,  p  eparation  of  in,  244 
Schroeder-Grillo  process,  229 

regeneration  of,  246 

testing,  243 

McKee,  Dr.  Ralph,  on  liquid  SO2,  41 
Melting  joint  of  sulphur,  41 
Mercury,  enemy  of  contact  process, 

2,  217 

Metallurgical  gases  for  SO2,  208 
Meters,  gas,  148 
Mist,  arsenic  carrier,  207 
Mixed     acid     to    introduce    nitric 

oxides    to    chambers,    141 
recovery  of  sulphuric  from, 

201 

testing,  176 

Moisture  in  contact  system,  217 
Dr.  Reese's  experiments,  230 
taken  from  air-quantity  of,  222 
Montejus,  122 
Mortar,  to  stand  acid,  96 


N 


New  Jersey  Zinc  Co.,  209 
Nitrate  of  soda,  characteristics,  47 

purification,  48 

testing,  176 
Nitre  cake,  disposal  of,  138 

testing,  176 
Nitre  losses,  183 

absorption  of,  115 

feed  control  of,  185 

introduction  of,  136 

methods  of  introducing,  138 

pots,  137 

potting  with  fuel,  139 

reactions,  136 
Nitric  acid,  16 

condensing  the  vapor,  141 

curve  of  boiling  points,  262 

in  mixed  acids,  202 


Nitric  acid,  lower  freezing  point  of 
H2SO4,  212 

production  in  chambers,  136 
Nitrogen  oxides — saving,  9,  10 
Nitrometer,  174 
Nitrososulphuric  acid,  9 
Nitrous  vitriol  in  the  Glover  tower,  98 

testing,  176 

O 

Oil  of  vitriol,  2 
Operation,  chamber  plant,  180 
Orsat  apparatus,  169 
Oxygen,    pure    in    contact    process 
unnecessary,  217,  234 

P 

Packing  for  Glover  towers,  98 
for  piping  and  valves,  213 
Pan  concentration,  186 
bottom  firing,  191 
temperatures,  191 
top  firing,  190 
Platinum,  2-5 

as  SO2  catalyzer,  228 
quantities  for  SO2  conversion, 

230 

stills,  199 
treatment  for  converter  mass, 

245 

Poison,  contact,  Opl's  theory,  13 
catalyzer  for  oxidizing  NH3,  150 
Dr.  Krause  theory,  3 
list  of,  217 
Pratt  fan,  161 

Preheaters,  Schroeder-Grillo,  232 
Priestly,  Dr.  Joseph,  2 
Production    to    figure   for   contact 

plant,  211 
Pulsometer,  122 
Pump,  acid,  127,  240 

makers,  240 
Purification    of    gases    in    contact 

process,  217 

Pyrites  cinder,  catalytic  action  of,  219 
burning,  53,  59 
fines  burners,  56 

Henerhoff  furnace,  57 
McDougal  furnace,  57 
Wedge  furnace,  61 


INDEX 


269 


Pyrites,  importation  of  Spanish,  32 

lump  burners,  55 

prices,  34 

properties,  45 
Pyrometers,  166 

dependent  upon,  210 

makers  of,  232 
Pyrrhotite,  45 

R 

Raschig,  theory  of  chamber  process, 

9 
Raw  materials,  44 

brimstone,  44 
chalcopyrite,  45 
galena,  46 
nitrate  of  soda,  47 
pyrites,  45 
pyrrhotite,  45 
spent  oxide  of  iron,  46 
zinc  blende,  46 
Reactions,  time  of,  in  chamber  pro, 

101 

are  exothermic,  101 
Reese,  Dr.  Charles  L.,  impurities  in 

contact  process,  11,  230 
Regeneration  of  contact  mass,  246 
Reich  test  for  SO2,  170 

made    regularly    in    contact 

process,  210 
tables,  173,  174 
Roebuck,  Dr.,  1 
Rule  of  thumb  methods,  182 


S 


Safety  appliances,  214 

Salt  cake,  17 

Saltpeter,  1 

Schroeder-Grillo  contact  process,  209 

catalyzer,  228 
Scrubbing,  need  for,  13 
Shut  down,  preparation  for,  of 

contact  plant,  215 
Silica  gel  for  recovering  SO2,  75,  228 
Silicon,  4 

tetrafluoride,   effect  upon  con- 
tact process,  11,  217 
Silver  in  lead,  173 


Sintering  pyrites  cinder,  68 
Soda  ash,  16 
Sodium  sulphate,  136 
Solubilities    of    sulphur   in   various 

solvents,  82 
Solution,  heats  of,  258,  259 

502,  best  percentage  for  conversion, 

211 

converting  to  SO3,  228 
first  step  in  making  H2SO4  tem- 
perature of  formation,  208 
slide  rule  for  conversion  of,  236 

503,  oxidation  of  SO2  to,  209 
converting  SO2  to,  228 
free  table,  255,  256 

in  burner  gas  causes  mist,  217 
total  table,  255,  256 
Specific  gravity,  table  of,  253,  254, 

255 

Specific  heat  and  heat  of  combus- 
tion, 41,  256 
Squire,  4 
Starck,  Joseph,  4 

process  eliminated,  208 
Steely,  James  E.,  on  SO2,  79 
Stoicometric  mixture  of   SO2  &   O 

won't  work,  234 
Strength  of  acid  to  make,  239 
Sulphur,  as  in  impurity  in  the  con- 
tact process  gas,  11 
impurities  in,  34 
in  the  U.  S.,  28 
Japanese,  45 
Louisiana,  34 

physicochemical  properties,  38 
prices,  34 
production  of,  31 
statistics, 
sublimated,  217 
uses,  36 

Sulphur  dioxide  characteristics,  7 
production  of,  49 
from  brimstone,  49 

metallurgical    processes, 

64 
Pyr  fines,  56 

lump,  55 
pyrite  cinder,  68 
zinc  ores,  67 


270 


INDEX 


Sulphur  dioxide  absorbtion  by  silica 

gel,  75 
liquid,  76 

character  and  uses,  77,  81 
Sulphuric  acid,  characteristics,  8,  16 
distribution     among     indus- 
tries, 18 

makers  in  the  U.  S.,  19,  27 
uses  and  production,  5,  16 
Sulphuric  acid,  electrical  resistance 
of,  260 


Tin,  effect  upon  lead,  192 
Towers,  acid,  various,  223 
Troy  compared  with  Avoirdupois 

weights,  245 

Twaddle's  hydrometer,  168 
Tyndall  test  for  dust  in  gas,  225 


U 


United   Alkali   Co.,   ammonia  still, 
148 


Tank  car  table,  250,  252 
Tanks,  storage,  120 

circulation,  222 
Temperatures  in  chambers,  checking, 

109 

Temperatures  for  absorbtion,  212 
for  burner  gases,  218 
for  scrubbing,  220 
heat   exchanger  concentration, 

195 

in  pan  concentrating,  191 
of  conversion  in  contact  process, 

230 
Tennessee    Copper   Co.,   acid  from 

met  gases  no  dream,  81 
chalcopyrite  as  of  sulphur,  46 

SO2  from  blast  furnace,  65 
Testing  contact  mass,  243 
exit  gas,  177 
gas,  166 

instruments,  166 
mixed  acids,  176 
nitrate  of  soda,  176 
nitre  Cake,  176 
nitrogen  oxides,  174 
nitrous  vitriol,  176 
Reich  test  for  SO2,  170 
Tyndall  test  (for  dust  in  gas), 

225 

Thermometers,  166 
Time  of  reaction  in  chamber  process, 
101 


Valves,  proper  ones  for  acid,  213 
Vapor  pressure  as  related  to  absorb- 
tion, 14,  212,  239 
curves   of   pressures   due   to 

water  and  SO3,  239 
of  sulphur,  38 
tables,  256,  257 

Virginia    Smelting    Co.,    producing 
liquid  SO2,  78 


W 


Ward,  Dr.,  1 

Water,  introducing  water  to  cham- 
bers, 109,  133 

effect  upon  contact  process,  11 
not  satisfactory  for  absorbtion, 
238 

Weber,  theory  of  chamber  process,  9 

Weight  of  acid,  curve,  263 

Wessel,  4 

White  lead,  3 

Winkler,  C.  I.,  4 

theory  of  chamber  process,  1 

Wollaston,  Dr.,  3 


Zinc  blende,  properties,  46 
ores,  SO2  from,  67 
effect  upon  lead,  192 


RE 
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